考考你的记忆力，根据句意及首字母补全在本课中出现的单词。

1.Walk s____  down the street and you'll find it.

2.Excuse me, can you tell me the way to the c_____?

3.I need a p______ of paper to write.

4.It's easy for us to be l ______ in the forest.

5.Walk on u ______ you reach the end.

若在电路的A点电位是10V；B点电位是一9V．则A、B两点间的电位差是19。