The boy is standing at the corner,He__(wait)for the bus. He __(wait)for the bus for half an hour.
问题描述：
The boy is standing at the corner,He__(wait)for the bus. He __(wait)for the bus for half an hour.
答
is waiting 正在进行的动作
has been waiting 已经进行并还在进行的动作
答
is waiting 正在等
has been waiting 已经等了一段时间了，也许还会持续等下去
答
第一个空填is waiting,表示他正在等公车,用现在进行时.
第二个空填has been waiting,表示他已经等了半小时了,而且这个动作还在继续,用现在完成进行时.