Critical Reasoning

Scientist: A controversy in paleontology centers on the question of whether prehistoric human ancestors began to develop sophisticated tools before or after they came to stand upright. I argue that they stood upright first, simply because advanced toolmaking requires free use of hands, and standing upright makes this possible.

Which one of the following statements, if true, most weakens the scientist's argument?

A) Many animals that do not stand upright have learned to make basic tools.

B) Advanced hunting weapons have been discovered among the artifacts belonging to prehistoric human ancestors who did not stand upright.

C) Many prehistoric human ancestors who stood upright had no sophisticated tools.

D) Those prehistoric human ancestors who first came to stand upright had no more dexterity with their hands than did those who did not stand upright.

E) Many of the earliest sophisticated tools did not require their users to be able to stand upright.

scientist's argument: Prehistoric human ancestors stood upright prior to the development of sophisticated tools.

What weakens the argument? Sophisticated tools were created before our prehistoric ancestors stood upright.
A) Who cares about many animals ... we only care about our prehistoric ancestors.

B) Correct.

C) Irrelevant.

D) How does this info weaken the scientist's argument? It doesn't.

E) Great ... but that still doesn't weaken the argument that prehistoric ancestors stood upright prior to the development of sophisticated tools.

Answer choice is B.

The official answer is B. But I don't understand why? Can anyone explain

Sure.

The question asks us to "weaken the scientist's argument" so we need to start this out by understanding the scientist's conclusion. It is: "Prehistoric human ancestors ... stood upright first."

Why? Because: Advanced toolmaking requires free use of hands, and standing upright makes this possible.

So the argument assumes that standing upright is the only way to get free use of hands. If this is true, only those prehistoric ancestors who stood upright could have developed tools.

However, answer choice (B) shows that this is not the case. Advanced hunting weapons have been discovered among the artifacts belonging to prehistoric human ancestors who did not stand upright.

Accordingly (B) is the answer choice that best weakens the scientist's conclusion.