词汇应用。

根据句子的意思及首字母的提示，填入适当的词，使句子完整、通顺。

1. The last day of a week is S________.

2. It's very d______ to swim in the river. Be careful, please.

3. My favorite subject is b______ because I like animals very much.

4. In the l_______, there are many books.

5. I like watching TV in my s______ time.

下列符号中，表示2个氢分子的是 

A．H₂

B．2H⁺

C．2H₂

D．2H