光网络单元Optical Network Unit（ONU）分类主要有（）。
A.MDU
B.SFU
C.HGU
D.SBU
参考答案：A, B, C, D
I would appreciate _____ if you could give me a ride home.[ ]
A. you
B. it
C. this
D. that
铁的光电峰为（）MeV。
A.1.712
B.2.223
C.7.135
D.7.646
