People are often uncertain about whether or not to use full stops in abbreviations. Here are some guidelines:

　　人们经常不确定到底什么时候要在缩写词后面加个点，什么时候不用。下文是使用规则：

　　1. In both British and American English, if you are using initial (i.e. first) letters to represent words, you don’t normally need to put a full stop after them:

　　在英国英语和美国英语中，如果缩写是从各单词的首字母得来的，通常无须加点，如：

　　BBC(British Broadcasting Corporation英国广播公司)

　　CNN(Cable News Network美国有线电视新闻网)

　　UK(the United Kingdom联合王国)

　　NATO(the North Atlantic Treaty Organization北大西洋公约组织)

　　IAEA(International Atomic Energy Agency国际原子能机构)

　　2. In American English, however, it is common to use a full stop as an alternative style for certain abbreviations, in particular:

　　但是，在美国英语中，有些缩写可以加点也可以不加点，如：

　　USA or U.S.A.

　　US or U.S.

　　3. If an abbreviation consists of the first and last letters of a word, you don’t need to use a full stop at the end:

　　如果缩写是由首字母和末尾字母组成的，则无须加点，如：

　　Mr(Mister先生)

　　Dr(Doctor医生)

　　4. If the abbreviation consists only of the first part of a word, then you should put a full stop at the end:

　　如果缩写只是某个单词开头的几个字母组成，则需要加点，如：

　　Wed. (Wednesday周三)

　　Dec. (December十二月)