包含原则，是指一个相对较大的时间范围内包含某个精确时间点，在这个精确的时间点发生了某个事件，则以精确事件为焦点，作为主句，置于句首，而关于时间范围的事件，沦为背景信息，作为从句或从属成分，在句中居于偏后的位置。下列句子中体现了该原则的是

A.The class began after the bell rang .

B.She was awake when he came.

C.It began to rain when I was watering the garden.

D.He heard a knock at the door while he was reading the letter.

正确答案：It began to rain when I was watering the garden.He heard a knock at the door while he was reading the letter.