There is "u" and "n" in the word "uncle". [ ]
A. a; a
B. an; an
C. a; an
D. an; a
答案:C
(1)21.6km/h= m/s ;
(2)5m/s= km/h ;
(3)15um= nm 。
夹杂物对钢性能有哪些影响?