根据首字母，填出正确的单词。

1. Don't s _____ in class. Keep awake, please.

2. A g ______ has a very long neck. It's a beautiful animal.

3. A dolphin is very i ________ because it can act as people do.

4. It has an u _____ face. We are afraid of it.

5. The panda is very shy, so please be very q ________.

现有KOH、H₂SO₄、Na₂CO₃、Ba（NO₃）₂四种溶液，将它们两两混合，其中的一种溶液只能发生一个反应，该溶液是（　　）

A．H₂SO₄溶液

B．KOH溶液

C．Na₂CO₃溶液

D．Ba（NO₃）₂溶液