Hi, LMS,
To determine what does and doesn't weaken the argument, let's focus first on the conclusion:
- The theory that the cave paintings depict the diet of the painters cannot be right.
Now why does the author think this? The author thinks these paintings cannot depict the diet of the painters because according to the author
- the painters would have needed to eat sea animals to survive the long sea journey AND
- there are no unambiguous paintings of sea animals
Next, ask yourself what it would mean to weaken this argument. To weaken this argument we'd need to find evidence that
even though there are no unambiguous paintings of sea animals and
even though the painters would have needed to eat sea animals to survive the long sea journey,
it might be possible that the theory that the cave paintings depict the diet of the painters
is right.
In effect, answer choice (C) mostly reiterates information we already know from the stimulus. From the stimulus, we know the paintings don't depict sea animals. If an answer tells us the paintings do depict land animals, this information does not address the gap in the reasoning between the information in the premises and the information in the conclusion. The information in answer choice (C) is at least consistent with the author's reasoning: the paintings are of land animals; the painters would have had to eat sea creatures to survive; therefore, the paintings cannot depict the painters' diet.
On the other hand, answer choice (D) contests the veracity of the author's first premise. If the painters had advanced meat preservation techniques, they might not have needed to eat the sea animals to survive the long journey, therefore
it might be possible that the theory that the cave paintings depict the diet of the painters
is right.
Thus (D) does in fact weaken the argument.
I hope this helps!