In this series, which number comes next?
5, 10, 6, 11, 7, 12, 8, 13,______

A. 12
B. 11
C. 10
D. 9

The pattern alternates between adding and subtracting.

The series begins by adding 5 to the first number to produce the second number, then subtracting 4 from the second number to produce the third. Then the pattern repeats.