NO.PZ2018101901000041
问题如下：
The “change in polarity” principle states which of the following?
选项：
A.Once an uptrend is broken, it becomes a downtrend.
Once a resistance level is breached, it becomes a support level.
The short- term moving average has crossed over the longer- term moving average.
解释：
B is correct.
请问A和C为什么不选呢
