Some microbiologists study bacteria in an effort to learn about the

Option A- All bacteria throughout evolutionary history have had a number of important features in common that are absent from other kinds of organisms.

If there are some features that have been common throughout the evolutionary history , it means that these features have not changed and so the microbiologists can study the modern/recently evolved bacteria and find out/learn something about the old ones.

I would recommend you to go through the OE Of OG 13 Q 43.

A is the best answer as we have to find the flaw in the criticism and not in the strategy of microbiologists.

It would be nice if no comments on right or wrong answers would be posted along the gmat questions, it makes the user unconsciously pick an answer based on those comments.

Premise: microbiologists study bacteria to learn about the structure of the earliest organic life
Conclusion : flaw in strategy as bacteria are extremely varied
Additional P: bacterium alive today is at the tail end of a long evolutionary process and has undergone considerable change since the earliest organic life appeared on Earth

We need to find an answer which weakens the additional Premise wherein something which says though bacteria varied still they are helpful to learn about the structure of the earliest organic life

A- All bacteria throughout evolutionary history have had a number of important features in common that are absent from other kinds of organisms - This answers helps my claim that though varied still helpful. Hold this one
B - Most ancient strains of bacteria either became extinct or adapted to changing environmental conditions - This supports the conclusion. Eliminate
C - All microbiologists study one kind or another of organic life - We are concerned about bacteria. Out of scope. Eliminate
D- Many microbiologists who study today’s bacteria do not draw inferences about the origins of organic life on the basis of their studies- This is a tempting answer. But we need an answer which supports that though bacteria varied still they are helpful to learn about the structure of the earliest organic life. Here no inference being drawn by microbiologists in a way supports the conclusion that they are not confident about their study. Hence NOT an answer.Eliminate
E- Even those strains of bacteria that have not significantly evolved in millions of years are importantly different from the first strains of bacteria that appeared on Earth- This answer is talking about some strains of bacteria and not all. But we need an answer will talks about ALL bacteria. So, eliminate

Hence A

i eliminated A just because it said "absent from other types of organisms"

we are comparing bacteria with other types of organisms.

how can this be right answer then?

i eliminated A just because it said "absent from other types of organisms"

we are comparing bacteria with other types of organisms.

how can this be right answer then?

For any CR question, it is convenient to categorise each part of the given passage into one of the following five categories:
1. Premise, 2. Conclusion, 3. Background, 4. Counter-premise, 5.Counter-point (i.e., opposite to conclusion)

For the subject question:

Some microbiologists study bacteria in an effort to learn about the structure of the earliest organic life : Background
A flaw in this strategy is that bacteria are extremely varied: Conclusion
Indeed, any bacterium alive today is at the tail end of a long evolutionary process and has undergone considerable change since the earliest organic life appeared on Earth: Premise

Premise ---> conclusion. In a "weaken" question we need to find the option that weakens the bridge between the premise to conclusion.

Here, the argument is as follows:
Bacteria today has undergone evolution and changed a lot (premise) ---> Therefore bacteria are varied (conclusion)

You would notice that in the passage, the strategy of the scientists comes only as background information - whether it is right or wrong has no bearing to the argument itself. The part "absent from other kinds of organisms" raises question about the strategy of the microbiogists - it is another flaw, but that flaw is not a part of the conclusion.

So option A weakens the Premise to Conclusion bridge used in the passage by stating that the bacteria are not varied.

Suppose the conclusion here would have been as follows:
A flaw in this strategy is that bacteria are extremely varied are different from other species.

In this case Option A could not have been the right option, becaused then it would have strengthened the argument.

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