单选题 Because it is not a serious problem, we are not necessary to take strict measures against the student.
【正确答案】 D
【答案解析】[解析] 本题考查结构应用。当动词不定式作主语时,常用it作为形式主语放在句首代替真正的主语,结构为it is+形容词(for sb.)to do sth.。所以,答案是D。