必修三以及必修四材料
e.g. The scientist has observed the stars all his life _____________________________. 这位科学家一生都在观察星星. 这位科学家一生都在观察星星. The police observed him go/going into the bank __________________________________ with a gun. _________. 警察看到他带着枪进入银行. 警察看到他带着枪进入银行. I observed that they were late. ⑵ n. _____________ observation