接线时，要用合格的电源线，电源插头、插座。电源线接头要用绝缘胶布包好。
参考答案：对
The old man,_______ abroad for 20 years, is on the way back to his mother land.
A．to work
B．working
C．having worked
D．to have worked
具有菌丝且菌丝内无典型细胞核的微生物（）。
A.霉菌
B.酵母
C.放线菌
D.螺旋菌
