电弧电流的本质是（）.
A.分子导电
B.离子导电
C.原子导电
D.电子导电
参考答案：B
11×40+39×48+8×11的值是（）。
A．3200
B．4800
C．2400
D．1200
— What is your sister?
— She is _________. [ ]
A. beautiful
B. a student
C. at home
D. doing her homework
