进行时除了表达“正在进行”的含义，还有另外两个用法：
一、代替将来时，表达“将来”含义
现在进行式表达“一般将来”，过去进行时表达“过去将来”。相比用将来时，用进行时表达将来显得较为随意和非正式。
1、When are we leaving and when are we coming back?
句意：我们什么时候走，什么时候回？相当于：When will we leave and when will we come back?
2、The clerk confirmed that his plane was leaving at nine o’clock.
句意：工作人员证实他的飞机将在9:00起飞。相当于： The clerk confirmed that his plane would leave at nine o’clock.
