Mr. Smith has two ________ , both of whom are teachers in a school.

A.brother-in-law

B.brother-in-laws

C.brothers-in-laws

D.brothers-in-law

答案及解析： D

解析：

解题思路：复合名词复数的构成方式有：1)将主体名词变为复数，如：fathers-in-law岳父，passers-by过路人，lookers-on旁观者；

2)无主体名词构成的复合词，在词尾加复数，如：grown-ups成年人，good-for-nothings无用的人，go-betweens中间人，look-outs守望者；

3)由man，woman，lord构成的复合名词应将前后两个词都变为复数形式，如：man doctor-men doctors，woman singer-women singers，lord mayor-lords mayors．