Critical Reasoning

Which of the following most logically completes the argument?

Bacteria might have developed on Mars early in its history.Theoretically, such Bacteria could have been to Earth by a meteorite.But , strains of bacteria from different planets would probably have substantial differences in protein structure that would persist over time.No two bacterial strains on Earth are sufficiently different planets.So if bacteria that originated on Mars were brought to Earth by meteorite either such bacteria died out or_____________.

A.other strains of bacteria were carried from Earth to Mars early in the history of Mars.
B.all bacteria now on Earth are descended from transported Martian bacteria.
C.meteorites are not the only means by which bacteria could have been transported between Mars and Earth.
D. the environment of Mars was more hostile for bacteria than was that of earth at the same time
E. any martian bacteria that did arrive on earth did so only after all bacteria had disappeared from Mars.



Experts could you pls help me to eliminate the option?

OA:B

Key to getting the right answer to a CR question is first understanding exactly what the prompt is saying.

In this case the prompt says that

- bacteria may have developed on Mars.

- such bacteria could have been transported from Mars to Earth by a meteorite.

- bacteria from two different planets would have persistent differences. In other word bacteria from Mars would continue to be distinguishable from bacteria that originated on Earth.

- no two strains of bacteria are as different as they would be had they originated on two different planets.

So, so far the prompt is saying that the bacteria on Earth are all too similar to have originated on two different planets.

Now here's the sentence that has to be completed.

So if bacteria that originated on Mars were brought to Earth by meteorite, either such bacteria died out or_____________.

That sentence seems to be about explaining how it could be that bacteria on Earth could have come from Mars given that the bacteria on Earth are all similar. Let's see how to complete it.

(A) This does not explain how the bacteria on Earth could all be similar even though bacteria that originated on Mars came to Earth.

(B) If true, this would explain how all the bacteria on Earth would be similar even if bacteria came from Mars, because bacteria from Mars would be the only source of bacteria now on Earth.

(C) This does nothing to explain how bacteria could have come from Mars and yet all bacteria on Earth are similar.

(D) This talks about what happened on Mars while not explaining the situation on Earth.

(E) This is about what happened on Mars, not what went on with bacteria on Earth.

So once you fully understand the prompt and where what it says is headed, it becomes pretty clear that the correct answer is B.

I have confusion in relation to option A.

Other strains of bacteria were carried from Earth to Mars early in the history of Mars

If all the bacteria on Mars were carried from Earth only then there would be no difference in the protein structures of the bacteria on Earth and those on Mars. Please tell me what is wrong with my approach.

aka12 wrote:I have confusion in relation to option A.

Other strains of bacteria were carried from Earth to Mars early in the history of Mars

If all the bacteria on Mars were carried from Earth only then there would be no difference in the protein structures of the bacteria on Earth and those on Mars. Please tell me what is wrong with my approach.

To get CR questions right, you have to notice key details.

There is in the argument a key detail that you have not taken into account. Before reading the rest of this post, you could go back to see what that detail is.

The easiest, most direct way to eliminate choice A is by noticing that the argument is about bacteria that ORIGINATED on Mars. So bacteria that originated on Earth, were transported to Mars and then were transported back to Earth are not what the argument is about. Notice also, that choice A talks about "other strains", which wording one can take to mean "strains other than those that originated on Mars."

Further, the argument is not about the degree of difference between bacteria on Earth and bacteria on Mars.

Also, getting CR questions right generally requires that you don't make up extended stories that are not clearly and logically supported by the prompts and answer choices. Running with the idea that answer choice A is about bacteria that were transported from Earth to Mars and then back again may be running to far beyond what is stated, though perhaps whether doing that would make sense given a different argument is debatable.