简介：请看这道试题:-Whatareyoudoingthere?-Nothing.-Nothing?You__.A.mustdosomethingB.mustbeuptodosomethingC.mustn'tbedoingnothingD.can'tdonothing.提供的答案为B。该题在设计上是个错误,beupto中的to只作为介词,不能看作不定式符号,后面不可接动词原形!
be up to后可接动词原形吗?
