It is clearly stated on the bulletin that ______ throws the rubbish away at will will be punished.
【正确答案】 D
【答案解析】这是一个复合句。句中it是形式主语，真正主语是that引导的从句，而that从句中又含有主语从句，此处应填入一个引导词引导该主语从句且在句中充当主语，符合这一要求的只有D。