根据对话内容，从方框内的选项中选出能填入空白处的最佳选项，其中有两个为多余选项。

A: Hey, Bruce! You seem unhappy.

B: Yes. I've just come back from the zoo.

A: Have you seen your favorite tigers?

B: Yes.

A: Why?

B: Because they had to stay in cages (笼子) and they were dirty.

A: I think they should go back to forests or mountains.

B: Even worse, a few children threw something at them.

A: That's too bad.

B: Of course. I also told them it was our duty to protect animals.

A: Protecting them is protecting ourselves.

A. I'm sorry to hear that. B. Did you stop them? C. But they didn't look well. D. When did you go to the zoo? E. Didn't you go to the zoo? F. How do you like tigers? G. What you did is quite right.