A:苯
B:苯乙烯
C:乙醇
D:1﹣己炔
—Excuse me, Maria. Can I use your bike?—Sure. Here you are. But you must return it _____ time.
一根圆柱形钢锭,长30厘米,管底面半径为1厘米,已知每立方厘米的钢重7.8克,这根钢管重多少克?