Researchers conditioned a group of flies to associate a particular odo

Researchers conditioned a group of flies to associate a particular odor with a weak electric shock. - A group of flies were conditioned to associate an odor with an electric shock.

Twenty-four and forty-eight hours later the researchers conducted tests on the flies, both individually and in groups, to determine whether the flies retained the conditioning. - The flies were then tested to check whether they retained the conditioning. Two sets of tests were conducted - 24 and 48 hours after the conditioning. The flies were tested individually and in groups.

When tested individually, the flies were significantly less likely to avoid areas marked with the odor. - Individual flies were less likely to avoid odor-marked areas. (“less likely” indicates a comparison. Less likely than whom? Logically, individual flies were less likely to avoid odor-marked areas than flies in groups.)

The researchers hypothesized that in the presence of the odor, a fly that retains the conditioned association gives off an alarm signal that arouses the attention of any surrounding flies, retriggering the association in them and thereby causing them to avoid the odor. - Based on their findings (previous statement), the researchers have come up with a hypothesis. They hypothesize that a fly that still has the conditioning gives off an alarm signal in the presence of the odor. This alarm signal grabs the attention of the surrounding flies. The surrounding flies’ association gets retriggered. And that’s why the other flies in the group also avoid the odor. (A fairly long-ended hypothesis.)

Gist:
Flies in groups avoid odor-marked areas more than individual flies. Why? The researchers came up with a hypothesis.
A fly that retains the association gives off an alarm signal.
An alarm signal leads to retriggering of the association. A retriggered association leads to flies’ avoiding odor.

1. What if the other flies avoided the odor-marked area simply because a fly gave off an alarm signal and they sensed something was amiss. The other flies need not have had the association retriggered in them.
2. What if there wasn’t even an alarm in the first place? Or, even if there was an alarm, what if the flies did not change course because of an alarm? There could have been some other reason that led to the other flies’ change of course.

We have already discussed a couple of gaps in the above section. Each pertains to an assumption. There could, of course, be other assumptions as well.


A. The flies do not give off odors as alarm signals.
Incorrect. Does the argument rely on what KIND of alarm signals the flies give off? Not at all. Moreover, even if the flies did give off odors as alarm signals, the hypothesis still holds as is.

B. Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group.
Correct. This is in line with the second gap we discussed above. The hypothesis requires this assumption. If flies avoided the odor simply because they were following other flies, the researchers’ hypothesis falls flat. This would mean that the other flies did not change their course because of an alarm signal. They were simply following other flies when tested in groups.

C. Flies that did not avoid the odor when tested individually were less likely than the other flies to avoid the odor when tested in a group.
Incorrect. Let’s first understand what this statement is saying. Let’s say that ‘flies “did not avoid” the odor’, implies flies flew into the odor. And, let’s try to tackle the way-too-many negatives in the sentence. We can rewrite the statement as:
Flies that flew into the odor when flying individually were more likely to fly into the odor when flying in groups than flies that avoided the odor when flying individually.

The sentence is essentially dividing the flies into two segments and then comparing the likelihoods of the two segments to fly into the odor. Now, we can understand that the flies that flew into the odor when flying individually needed some external trigger (such as an alarm signal) to avoid the odor. But after they got the trigger, do we really care whether they avoided more, less, or equally the odor compared with the other segment of flies? The argument is based on an overall likelihood of flies to fly into the odor, not likelihoods of different segments of flies. Thus, this option does not have an impact.

D. Prior to their conditioning, the flies would likely have found the odor used in the experiment to be pleasant.
Incorrect. How flies found the odor prior to the conditioning is irrelevant to the hypothesis.

Even if somehow we do not see the irrelevance, we can see that it is not necessary for the flies to have found the odor pleasant prior to the conditioning for the hypothesis to hold. The hypothesis would hold as is even if the flies did not find the odor pleasant before their conditioning.

E. An electric shock was used during the flies' conditioning and during the later tests.
Incorrect. We already know that an electric shock was used during the flies’ conditioning. Thus, the new information that this option gives is that an electric shock was used during the later tests as well. If in the later tests an electric shock was used, we start to wonder whether the flies responded the way they did because of their conditioning towards the odor, or because of the electric shock used? If an electric shock was used during the later tests, it is possible that, while in groups, a fly that got the shock gave an alarm signal to others. In this case, the fly that gave off the alarm signal had not retained any conditioned association and the alarm signal just warned the other flies and not retriggered their association. Thus, this option rather weakens the argument and thus cannot be an assumption.



SC Notes:

Let’s break down the last sentence of the passage to understand the modifiers better.

• The researchers hypothesized that (Main Clause)
  
  1. in the presence (Prepositional Phrase modifying the verb “gives off”)
  
  • of the odor, (Prepositional Phrase modifying “presence”)
  2. a fly (Subject of the ‘that’ clause)
  
  • that retains the conditioned association (Another ‘that’ clause modifying ‘fly’)
  3. gives off an alarm signal (“gives off”: verb for the subject ‘fly’
  
  • that arouses the attention (‘that’ clause modifying ‘alarm signal’)
    
    • of any surrounding flies, (Prepositional Phrase modifying “attention”)
    • retriggering the association in them (Comma+Verb-ing modifier modifying the previous clause ‘that arouses…’)
    • and thereby causing them (Comma+Verb-ing modifier modifying the previous clause ‘that arouses…’)
      
      • to avoid the odor. (Infinitive Phrase modifying “causing”)

If you have any doubts regarding any part of this solution, please feel free to ask.