words:
parcel，包裹
detective，侦探
expect，期待
airfield，飞机起落的场地
guard，警戒，守卫，n
precious，adj，珍贵的
stone，石头
expressions：
keep guard，守卫
to one's surprise，令某人吃惊
过去进行时:
When I was watering the garden, it began to rain.
I was having breakfast when the telephone rang.
While we were having a party, the lights went out.