In a data group, when the numbers are arranged from smallest to largest, if the number of terms in the group is odd, the median is the middle number; if it is even, the median is the arithmetic mean of the two middle numbers.
Let $A$ and $B$ be two sets. From the number of elements of the sets $A$, $B$, $A \cap B$, $A \cup B$ and $A \setminus B$, the numbers in the data group are arranged from smallest to largest as
$$s(B),\ s(A \cap B),\ s(A \setminus B),\ s(A \cup B),\ s(A)$$
in this form.
If the arithmetic mean of this data group is 5, what is the median?
A) 3
B) 4
C) 5
D) 6
E) 7