Few students could understand the sentence until it ________ by Miss Chen.
explained
was explained
was explaining
The telephone _______ by Alexander Graham Bell.( )
A.was inventedB.invents
C.invented
I _______ Anna since three years ago.( )
A.knewB.knowC.have known
If I go to the movie, I _______ my homework on time.( )
A.didn't finishB.don't finish
C.won't finish
I like Chinese, _______ I don't like math, because it's not easy to learn it well.( )
A.andB.butC.or
I think it's impolite _______ others waiting.( )
A.to keepB.keepingC.keep