:
He suddenly fell ill yesterday.
昨天他突然生病了。
The engine stopped because the fuel was used up.
发动机因燃料用光而停机了。
b)表示过去经常发生的动作或存在的状态。
I wrote home once a week at college.
我上大学时每周给家里写一封信。
He was already in the habit of reading widely in his boyhood.
他童年时就养成了广泛阅读的习惯。
注：表示过去的习惯性动作，除了用过去时外，还可以用used to或would来表示。
She used to study late into the night when she was in Senior Three.
她上高三时经常学习到深夜。
