连字符（hyphens）
1、当数字（21-99）或分数用作修饰语时，使用连字符。
forty-two strudents
three thousand five hundred and sixty-seven students
two-thirds majority (vs. "two thirds of the voters")
2、当复合形容词前置修饰名词时，使用连字符。
a well-liked author
an author who is well liked
a world-renowned composer
a composer who is world renowned
3、用于前缀ex-, self-, all-后缀elect-以及专有名词或专有形容词前缀之前。
all-star
ex-mayor
pro-choice
self-image
non-European
senator-elect
4、用于复合短语，注意：当描述年龄时，短语用作形容词时需要使用连字符，数字用作形容词时不需要使用连字符。
the nine-year-old boy
He is nine years old.
sister-in-law
all-or-nothing
up-to-date
soon-to-be
5、注意连字符将改变句子的意思。
a hot-water bottle (a bottle for holding hot water)
a hot water bottle (a bottle of water that is hot)
to re-press a shirt (to iron again)
to repress bad memories (to keep at bay)