In this simple alternating subtraction and addition series; The first series begins with 5 and adds 2; the second begins with 15 and subtracts 3, and so on.
Fill in the blank with the correct number in this number series: 5, 15, 7, 12, __, 9, 11,... ?
A) 6
B) 9
C) 8
D) 7
E) 5