Out of all the pronouns, "whom" makes the most sense grammatically. This allows us to narrow it down to A or D.
In order for it to be the object of a preposition, there would have to be a preposition in front of it. "For," however is <em>not</em> a preposition. In fact, there isn't a preposition in the whole question.
This leaves us with option D, which is the correct answer.
You can better tell it's a direct object if you flip the sentence around a bit.
Your sister is waiting <em>for whom</em>?
"Whom" is essentially receiving the action. "Whom" is what your sister is waiting for.
Answer: D. whom; direct object.
I would choose B) as the answer
B. Because a particular word may have multiple meanings.
E.g. I will PARK the car.
Let's go to the PARK.
Answer: A) Playful.
Explanation: the mood of a character in a story is the attitude of the character towards a situation of another character. In the given excerpt from "Mending Wall" the speaker has a playful mood towards his neighbour and the situation where he was asked to build a wall, and he doesn't understand what is the point. To express his point of view he asks questions and he has a playful attitude.
