harry up.He___for us at the station.A must wait B must be waiting C should wait

问题描述:

harry up.He___for us at the station.A must wait B must be waiting C should wait

B must be waiting
肯定正在等be doing不是即将吗?在这里是什么用法?为什么要用be waiting这里是含情态动词的现在进行时态,其谓语部分的结构为:情态动词 + be + doing