涡桨发动机组合了涡喷发动机的优点和螺旋桨在低速时（）高的特点.
A.有效功率
B.推进效率
C.最大功率
D.拉力
参考答案：B
The earthquake ______ when I _______some cleaning.
A．starts, was doing
B．started, was doing
C．was starting, was doing
D．starts, were doing
Ff的高速现场总线HSE的通信速率为100Mbps，信号类型为电流和电压信号。
