12：woman-doctor的复数形式是women-doctors，但coat-hanger的复数形式是coat-hangers，而不是 coats-hangers。请问转化时有什么规则可循吗？

Question 12: I find it odd that the plural form of "woman doctor" is "women doctors" while the plural form of "coat-hanger" is "coat-hangers" instead of "coats-hangers". Are there any rules I can keep when I need to change these words into a plural form?

Answer: Such words are called compound nouns. We may use the following methods to change them into plural forms:

1). Change both of the two words into their plural forms. It is widely used when the compound
noun is composed of words such as "man" and "woman". Eg. man-servant → men-servants;
woman-doctor → women-doctors.
2). Change the first word, which is the central part of the compound noun, into its plural
form. Eg. passer-by → passers-by; looker-on → lookers-on.
3). Change the second word, which is the main body of the compound noun, into its plural
form. Eg. coat-hanger → coat-hangers; boy-friend → boy-friends.
4). Change the last word into its plural form when there's no main body in the compound
nouns. Eg. sit-in → sit-ins; grown-up → grown-ups.

问题12：我觉得很奇怪，woman-doctor的复数形式是women-doctors，但coat-hanger的复数形式是coat-hangers，而不是 coats-hangers。请问转化时有什么规则可循吗？

回答：这些词我们称之为复合名词。复合名词的复数形式可采取以下几种形式：

1). 第一个和第二个词都变为复数，这通常用于有man或woman出现的复合名词。
如：woman doctor → women doctors, man-servant → men-servants
2). 第一个词(复合名词的主体）变为复数。如：passer-by → passers-by, looker-on → lookers-on
3). 第二个词（复合名词的主体）变为复数。如：coat-hanger → coat-hangers, boy-friend → boy(-)
friends
4). 若没有主体，第二个词变为复数。如：sit-in → sit-ins, grown-up → grown-ups。