题目内容：

Who's that boy reading in the garden?Is it David?It( )be David.I saw him in the
Who's that boy reading in the garden?Is it David?
It( )be David.I saw him in the classroom just now
A.must B.can't C.may D.shouldn't

优质解答

B　不可能是（　否定句中的猜测用can't）