A:should have failed
B:might have failed
C:couldn’t have failed
D:mustn’t have failed
如图所示为电流与电压的关系图像,由此可以判断( )
3×2=____2×2=____1×4=____ 4×2=____
对外开放过程中,重庆成为对外开放城市的时间是在( )