名人教英文：punctuations 标点符号
punctuations serve to disambiguate the meaning of a given sentence. in other words, punctuations represent a logical thinking process which makes the meaning of a written sentence intelligible. 标点符号是用来解明某句子的意思。也就是说，标点符号代表有逻辑的思维，令写下的语句容易明白。
by convention, the ten most commonly used punctuations are identified below.
以下是十个惯用的标点符号。
apostrophe (')
this punctuation mark is used in the following circumstances:
1. to show possession in different ways:
the apostrophe before the "s" shows a single possessor. e.g. the boy's car is outside.
if the apostrophe is written after the "s", it shows plural possessors. e.g. the boys' car.
however, when the plural ends in "en", as in the word "children", the apostrophe is placed before the "s":
e.g. children's car.
2. to show abbreviation so as to link two words:
e.g. it's a car outside.
"it's" is an abbreviation of two words: it is.
abbreviations are also found in words such as shan't, won't, couldn't, shouldn't which can also be written as shall not, will not, could not, should not.
3. to show plurals to a letter or a number:
e.g. the last time i sat for the examination, i got ten a's in english and five 9's in mathematics.