根据句意和汉语注释,在答题卷标有题号的横线上,写出单词的正确形式。

1.  It is very important for children to learn to be ________ (有礼貌的).

2.  What is the ________ (高度) of the building over there?

3.  Different people have different ________ (能力) to do different things.

4.  He ________ (重复) his words to make himself understood at yesterday's meeting.

5. The Greens had a ________ (令人愉快的) trip to Beijing last week.

C语言中的标识符分为关键字、预定义标识符和用户标识符，以下叙述正确的是( )。

A) 预定义标识符(如库函数中的函数名)可用做用户标识符，但失去原有含义
B) 用户标识符可以由字母和数字任意顺序组成
C) 在标识符中大写字母和小写字母被认为是相同的字符
D) 关键字可用做用户标识符，但失去原有含义