用墨汁写字绘画,日久仍不褪色,这是因为碳在常温下( )
A:易被氧化
B:化学性质不活泼
C:是黑色固体
D:容易获得
— Waiter, I'd like a hot wing hamburger and corn salad.
— Sorry, sir. They ________ only for lunch and dinner. Why not consider ________ something else?
如图所示,用轻质杆将一电灯吊起,O点是支点.请画出动力F1的力臂L1和阻力F2的示意图.
图中路灯安装太阳能电池板最主要的目的是( )