单选题
-- There is a bad smell here. -- Oh, dear! I ______ the gas.
[A] must forget turning off
[B] must forget to turn off
[C] must have forgotten turning off
[D] must have forgotten to turn off
【正确答案】
D
【答案解析】[解析] 本题考查情态动词表示推测。推测已经发生过的事情，用 must have done。forget to do sth．表示忘记去做某事(事情没有做)；forget doing sth．表示忘记做过某事(事情已做)。第一句指出，“这里有一股难闻的气味”，由此推知，“我”一定是“忘了”关煤气了。