1.  AB, DEF, HIJK, ?, STUVWX

A. LMNO
B. LMNOP
C. MNOPQ
D. QRSTU

Answer: Option C

Explanation:

The number of letters in the terms of the given series increases by one at each step.The first letter of each term is two steps ahead of the last letter of the preceding term.

However, each term consists of consecutive letters in order.