They can’t have been doing their homework ---doing是什么词性?have been 在这里还是表现在完成时吗
问题描述：
They can’t have been doing their homework ---doing是什么词性?have been 在这里还是表现在完成时吗
答
doing是do的进行式哈,不是词
have been doing是完成进行时,意即：他们不可能现在还在忙着他们的作业