选择A.
根据题意,由于天上乌云密布,则大雨将至,且这是说话者主观判断的.所以选A而非C.在此附上两者区别.
be going to与will的区别
be going to与will两者都可表示将要发生的事、将要去做某事,但它们有如下几点区别:
1. be going to 表示近期、眼下就要发生的事情,will 表示的将来时间则较远一些,如:
He is going to write a letter tonight.
He will write a book one day.
2. be going to 表示根据主观判断将来肯定发生的事情,will表示客观上将来势必发生的事情.
He is seriously ill. He is going to die.
He will be twenty years old.
3. be going to 含有“计划,准备”的意思,而 will 则没有这个意思,如:
She is going to lend us her book.
He will be here in half an hour.
4.在有条件从句的主句中,一般不用 be going to, 而多用will, 如:
If any beasts comes at you, I'll stay with you and help you