Bank A B C D E F G H I

Bank A B C D E F G H I
Number of Branches 20 12 39 36 28 25 28 10 21
The table above lists the number of branches for each of the nine banks in Region X.What is the median number of branches for the banks in this region?
A 25
B 26
C 27
D 28
E 29
我算出来是A,问下应该怎么理解啊.
是美国5月份寄来的考题，$18的，一般不可能有问题的啊