题干
— Be quiet, the head teacher Mr. Gu is coming.
— Don't worry. It _____ be him. Mr. Gu is much fatter.
A：mustn't
B：may not
C：needn't
D：can't
答案(点此获取答案解析）
D
— Be quiet, the head teacher Mr. Gu is coming.
— Don't worry. It _____ be him. Mr. Gu is much fatter.
A：mustn't
B：may not
C：needn't
D：can't
,
(如右上图);当甲,乙行走的速度相同(不为零)时刻: