8. A number like 45132 is called a "wave number", meaning the tens and thousands digits are larger than their adjacent digits. The number of five-digit "wave numbers" that can be formed with the digits $1,2,3,4,5$ without repetition is
A. 20
B. 18
C. 16
D. 11
If the tens digit and the thousands digit are 4 and 5, the number of five-digit "wave numbers" with non-repeating digits is $A_{2}^{2} \cdot 6=12$; if the tens digit and the thousands digit are 3 and 5, the number of five-digit "wave numbers" with non-repeating digits is $A_{2}^{2} \cdot 2=4$. Therefore, the answer is $C$.