光在不同介质中的传播速度一般不同,光在 中的传播速度最大,在我们的计算中取 m/s.
真空;3×108
-It's generous_______ him to provide the poor children so much food.
-Yes. I think he is the person that we should admire very much.
A.of; for
B.for; to
C.for; with
D.of; with
旅游区(点)的质量等级的评定应严格按照“自检、______、初评、______ 、审批、______”的程序进行。