2. 现在进行时
表说话时或目前一段时间内正在进行的活动；与频率副词，如always，constantly，continually，again等连用，表示说话人的某种感情色彩（赞叹、厌烦、埋怨等）。
We are having English class.
The house is being built these days.
The little boy is always making trouble.
考点一：在时间状语或条件状语从句中表示将来正在进行的动作。
Look out when you are crossing the street. ...
