从方框中选择合适的选项补全对话。

A: Where have you been, Li Hai? I called you, but you weren't in.

B: ____

A: ____

B: I found that the factory was pouring waste water into the river near it. Lots of fish have died.

A: ____

B: Do you think “Greener China” can do something?

A: ____ if they know about this thing, they will prevent it. Let's write to them at once.

B: ____ I think everything will become better.

我国古代炼丹家发明的火药很早就用于军事，下列战争中最不可能使用火药武器的是（    ）

读“世界洋流分布局部图”，回答下题．

听下面一段独白，你会看到4个问题和相关的选项。请从每个问题A、B、C三个选项中选出最佳选项。

20种氨基酸的平均相对分子质量为128，假若有一个多肽化合物，由10个氨基酸构成一个肽链，那么该多肽的相对分子质量和至少含有的氨基数目分别是   (　　)