问题

How the fire in the dancing hall started _________ a mystery

A:to remain
B:remains
C:is remaining
D:is remained

正确答案是：

同类题型

Our teacher often warns us ________ on theroad.

People in the west make _____ a rule to buy Christmas presents for their relatives and friends. [ ]

She ____________ as an animal trainer since 2003.

I smell something ________ in the kitchen.Can I callyou back in a minute

I fell and hurt my leg just not.—_______.