细菌约占粪便于重的多少（）
A.1／3
B.1／2
C.1／4
D.2／3
E.1／5
参考答案：A
On his way to the airport,it________him all of a sudden that he had forgotten his passport.[ ]
A．hit
B．knocked
C．occurred
D．beat
100mW等于（）dBm
A.40
B.33
C.20
D.30
