带上自救器后，自救器外壳逐渐变热，吸气温度逐渐升高，表明自救器工作不正常。
参考答案：对
人类较早发现和利用的一种金属是______
A．金 B．银C．铜 D．铁
_______ I take part in a group discussion or try to speak English to someone, I find it difficult to express myself.
A．If only
B．Every time
C．Now that
D．In case
