Researchers conditioned a group of flies to associate a particular odo

Sharing my 2 cents here:

Conclusion : A fly that retains conditioning gives off an alarm for others to avoid the odour when moving in a group.

Evidence : When flies were tested individually, they were less likely to avoid the odour hence the hypothesis that they give off an alarm when travelling in a group (It is not given that they tend to avoid the odour frequently or less frequently when travelling in a group)

Option A - The flies do not give off odors as alarm signals.
This would be undermining the information given in the passage so straight eliminate

Option B - Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group.
This actually means that flies ran into the shock were not following another group of flies. if they were following a group then they should have avoided the shock as per the hypothesis. Hence this would be a necessary assumption as it would break the hypothesis - ANS

Option 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
Rephrasing this in my own works - Flies that ran into the shock had less chances to run into the shock again than other flies when tested in a group.
It is comparing flies individually and in a group & the hypothesis is only limited till a group - eliminate

Option D - Prior to their conditioning, the flies would likely have found the odor used in the experiment to be pleasant
Even if they found the odour to be pleasant then the conditioning should have changed that so this does not make sense - eliminate

Option E - An electric shock was used during the flies' conditioning and during the later tests
The later tests do not have relevance in this argument, and we already know that electric shock was used for these tests so this is not new information - eliminate

Thank you! - open to views