压缩机如采用（），阀头易损，损坏后更换即可。
参考答案：蘑菇阀
牙科用铸造合金中，低熔合金是指熔点低于（ ）。
A．500℃
B．600℃
C．700℃
D．800℃
E．900℃
The teacher asked me _____.
A．that I had finished my homework
B．that had I finished my homework
C．whether had I finished my homework
D．if I had finished my homework
