根据短文内容和首字母的提示，把所缺单词完整地填写在短文后的横线上。

Nowadays, it’s common to keep dogs as pets. We can often see dogs’ owners taking them for a walk. But have you h 小题1: of taking penguins for a walk? Here i 小题2:  a piece of news from Japan. In Tokyo Zoo, penguins go out for a walk in line every day. It is said that this can make them happy and stop them from being homesick(想家的).The penguins in the zoo didn’t eat as

w 小题3: as they did in South Pole(南极) and they were u 小题4: to the keepers when they first got to the zoo, maybe they were not used to the life in the zoo. So the zoo keepers c 小题5:  up with this good idea. They just let them walk as they did in South Pole. Now, all these penguins have become happy.

比重最轻的煤气是（）。

A.高炉煤气

B.焦炉煤气

C.空气－蒸气煤气