焊接无线电元器件、安装导线时应选用（）锡铅焊料。
A.58-2
B.39
C.68-2
D.80-2
参考答案：A
—I drove to Zhuhai for the air show last week.
—Is that ________ you had a few days off ?
A．where
B．when
C．what
D．why
热机是把______能转化为______能的机器，四冲程内燃机的______冲程实现了这一能量转化．
