用铝脱氧后，随着精炼过程的进行钢液中溶解氧含量会（）。
A.升高
B.降低
C.不变
D.有时升高、有时降低
参考答案：A
The supermarket _____ since last year. [ ]
A. opened
B. was open
C. has opened
D. has been open
为什么充电架要接地？
