某段光纤长25km,用切断法测试时已知,求此段光纤的平均衰减为()。
A.0.24dB/km
B.0.25dB/km
C.0.26dB/km
D.0.27dB/km
参考答案:A
Mr. Zhang is the best music teacher in our school, but he has hurt his left foot and cannot ________tomorrow’s concert.
A.take part
B.play a part in
C.participate
D.participate in
关于往复式压缩机气阀故障,下列说法正确的是()。
A、气阀温度升高
B、气阀温度降低
C、出口压力下降
D、压缩机处理量提高聚物