Imagine the situation in which the given arrangement is placed inside a trolley that can move only in the horizontal direction,as shown in the figure. If the trolley is accelerated horizontally along the positive $x$-axis with $a_0$,and if $a_{min}$ and $a_{max}$ are the minimum and maximum values of $a_0$ for which the blocks remain stationary with respect to the surface,then identify the correct statements.

• A
  If $a_0 < a_{min}$,the block $m$ accelerates downward.
• B
  If $a_0 > a_{max}$,the block $m$ accelerates upward.
• C
  The block $m$ does not accelerate up or down when $a_{min} \leq a_0 \leq a_{max}$.
• D
  All of the above.