When the movie ends, what the oak tree does at the theater is that it leaves. This is a pun supposed to have a humorous effect on the listener or the reader - usually, when a movie ends, people leave the theater. However, since this is a tree, and it's got leaves, you can understand the correlation between the two words.
The answer is b. because this way you can hear all the characters thoughts and what they are saying. this lets you know how they truly feel versus how they want you to think they feel.
