问题如下：
Which of the following is not a component to construct Bollinger Bands?
选项：
A.a moving average line for a period
B.the upper and lower lines deviated at the same level from the moving average.
C.the uptrend and downtrend line across the moving average line.
解释：
C is correct.
Bollinger Bands includes the followings parts:
1)a moving average of a certain period;
2)a upper line representing the moving average plus a set number of standard deviations from average price;
3)a lower line that is a moving average minus the same number of standard deviations.
老师 这道题为什么A可以选
