锅炉应由哪三项安全装置？
参考答案：
有可靠安全阀、压力表、水位表。
---Thank God! The accident was avoided after all.
---That was lucky, but ten inches nearer and the two cars ________. [ ]
A. were destroyed
B. would be destroyed
C. would have been destroyed
D. had been destroyed
验电器的作用是______，它是根据______的原理制成的．
