—That must be Mr. John.
—No, it ________ be him. I saw him off at the airport half an hour ago.
A:may not
B:mustn't
C:can't
D:needn't
央视的《中国汉字听写大会》首播后就登顶微博热门话题榜,随即全国兴起了“国学热”这是因为( )
We must thank trees ____ oxygen into the air .
科学的研究方法是取得成功的关键。下列关于人类探索遗传奥秘历程中的科学实验方法及技术的叙述,不正确的是