题干
—Look! The lights in the teachers’ office are still on. Is Mr. Li working?
—No. It _______ be Mr. Li. I saw him leave just now.
—No. It _______ be Mr. Li. I saw him leave just now.
A：may not
B：mustn’t
C：can’t
D：needn’t
答案(点此获取答案解析）
C
，且
是函数
的导函数，则
（ ）