A:铁
B:碳
C:氧
D:钙
I'm afraid ____ out alone at night.
____ ____The city____ ____ in ten years?
车轮周长一定,所行驶的路程和车轮的转数成____比例.
用公式法解x2+3x=1时,先求出a、b、c的值,则a、b、c依次为( )