维生素C注射液中各成分的作用分别为：NaHSO3（）.
A．pH调节剂
B．抗氧剂
C．金属络合剂
D．溶剂
E．主药
参考答案：B
My father _______________ in a factory. [ ]
A. work
B. works
C. working
D. worked
There have been several new events ______ to the program for the 2012 Olympic Games.[ ]
A. add
B. to add
C. adding
D. added
