saurabhmahajan wrote:Why the OA is D (marked in RED) ?
IMO: A

Saurabh,

This is a very typical cause & effect problem.

The evidence states that couples having different sleep & waking cycles have more violent arguments. This gives us the impression that the difference in the sleep & waking cycles is the cause and the violent arguments and unhappy life is the effect.

Since this is a weakens the argument question, we are looking for evidence that will counter the above cause & effect relationship.

D does precisely this by flipping the cause & effect. D suggests that people who are already in unhappy marriages express hostility to their spouses by intentionally adopting different sleeping & waking cycles. Or in other words, the effect mentioned in the original evidence (unhappy marriages) is actually the cause while the cause in the original evidence (different sleep cycles) is really the effect.

A does not weaken the argument because it merely states that couples sharing the same sleeping & waking patterns also occasionally have arguments. This has little bearing on weakening the argument as significantly as option D .

Hope the explanation was clear and helped!!

Cheers!