Choose the missing terms out of the given alternatives : 2, A, 9, B, 6, C, 13, D, ?

Explanation:-

The given sequence is a combination of two series:
I: 2, 9, 6, 13, ? and
II: A, B, C, D
The pattern in I: is : 2 + 7 9 - 3 6 + 7 13 - 3 10
So, the missing term is 10.