主动改被动：
who did you wait for a moment ago ?(who was waited by you for a moment ago?)
who did he hear coming here ?(who was heard coming here by him?)
Mrs Smith always buys her son a big birthday cake on his birthday ?(两种）
(Mrs Smith's son is always bought a big birthday cake by his mother on his birthday.)
(A birthday cake is always bought to her son by Mrs Smith on his birthday.)
who will do the work?
(By whom will the work be done?)
Engilsh_is__ _regarded___ _as__ a first language __by__ most people in the USA . Most people in the USA _regard___ Engilsh __as___ a first language.