英语单选1
He had been kocking at the door for a long time but no one came to open it . He said himself,"No one ___ indoor"
选CAN BE 为什么不选MUST BE,SHOULD BE
参考答案:可以这么说吧，must be和should be多表示比较肯定的语气，而因为他是在外边敲门，对屋内情况并不了解，所以只能选表猜测语气的短语即can be.（另：He had been knocking at the door是过去完成进行时，用英语说是Pastence Perfect Continous,indoor是室内的意思 ）