问题补充：
Look , dark clouds are gathering. It is to rain.
A. possibly
B. probably
C. likely
D. perhaps
答案：
A. possibly
B. probably
(答案→)C. likely
D. perhaps
解析：probably,possibly,perhaps都是副词,均不能作表语。likely为形容词,可作表语,此题用的句型是be likely to…意为“有可能要……”。题意为“看,乌云密集,很有可能快要下雨了”。故正确答案为C。
温馨提醒：probably指“多半”,其可能性超过一半; perhaps和maybe指“或许”,其可能性大致为一半; possibly仅指“也许”“有可能”,其可能性低于一半。例如:
Probably he will succeed.他很可能会成功。
Perhaps〔maybe〕 he will succeed.他也许会成功。
He will possibly succeed.他有可能成功。
2.maybe比perhaps更口语化,且要用于句首; perhaps可用于句末、句中、句首; probably多用于句中。
3.maybe和possibly可用于礼貌的建议或请求,另三个词无此义。例如: Could you possibly lend me 1000 yuan ?你能借给我1000元钱吗?
