Select the letter that can replace the question mark (?) in the following series.
A, C, E, G, I, K, ?

Correct option is D

The given series is:
A, C, E, G, I, K, ?

Each letter is increasing by a gap of 2 in the alphabet:

• A (+2) → C
• C (+2) → E
• E (+2) → G
• G (+2) → I
• I (+2) → K
• K (+2) → M

Thus, the correct answer is D (M).