频率合成器工作和显示正常但发射机不工作，说明最大可能是（）。
A.失锁判断电路
B.失锁禁止电路
C.VCO
参考答案：B
-----Tom. You look very bored and tired.
-----Yes, I ______ my father on the farm until seven o’clock this morning.
A．have been helping
B．had helped
C．was helping
D．am helping
—Have you ________ him to keep good hours? —Yes, I have. But he doesn’t listen to me.
A．advised
B．suggested
C．agreed
D．persuaded
