题目内容：

单词拼写(共5小题; 每小题1分, 满分5分)

根据首字母或汉语提示，在句子中填入适当的单词。

1.Bamboo grows up straight and thin, with b____ at the top.

2. He had attempted to rescue the _____（溺水的）man.

3. The i_____ of the computer marked the beginning of a new era.

4.A red light is usually a _____ (信号) of danger.

5.John is _____ (订婚) to Mary.