完美无谐波变频系统构成为()。
A.高→低→变频器→高→电机
B.高→变频器→高→电机
C.高→变频器→低→高→电机
D.高→变频器→低→电机
参考答案:B
用所给动词的适当形式填空。
1.Listen! How wonderfully the girls _________ (sing)!
2.Simon will leave here if he _________ (finish) the work tomorrow.
3.________ you ________ (go) to the World Park in Beijing next week?
4.—What did you do last night?
—I _________ (write) a letter to my parents.
5.The zookeeper told them __________ (not leave) litter there.
柴油发动机喷油提前角过大,不仅会造成发动机启动困难,功率下降,油耗增大,而且会使发动机()。
A、着火延迟期缩短、排气温度降低
B、着火延迟期延长、工作粗暴
C、着火延迟期缩短、排气温度升高
D、着火延迟期延长、补燃严重