高速转动的机械、输送带长时间运转，与环境中的煤粉、矸石等摩擦起火。
参考答案：对
I __Xiao Mao since she was a little girl.
A．know
B．knew
C．have known
D．had known
原子是由原子核和核外＿＿＿＿组成，原子核是由带正电的＿＿＿＿和不带电的＿＿＿＿组成
