二氧化碳在空气中含量达到()时,能使一般可燃物质的燃烧逐渐窒息。
A.30%~35%
B.35%~40%
C.40%~45%
D.45%~50%
参考答案:A
The teacher asked me if _____ finished my homework. [ ]
A. I have
B. have I
C. I had
D. had I
交流耐压试验规定试验电压一般不大于出厂试验电压值的()。
A、70%
B、75%
C、80%
D、85%