Explanation:

Let's break this series down step by step:

- The given series is: AYC, EUG, IQK, MMO, ?

- Check how each letter progresses from one group to the next.

First letters:

A (1), E (5), I (9), M (13)

Each is moving forward by 4 in the alphabet:

A+4=E, E+4=I, I+4=M, M+4=Q

So, the next should start with Q.

Second letters:

Y (25), U (21), Q (17), M (13)

Each goes backward by 4:

Y-4=U, U-4=Q, Q-4=M, M-4=I

The next should be I.

Third letters:

C (3), G (7), K (11), O (15)

Each is moving ahead by 4:

C+4=G, G+4=K, K+4=O, O+4=S

So, the next is S.

So, putting it all together, the answer is QIS.

Option 2: QIS

Here’s a quick note on the other options:

- Option 1 (IQS) and 3 & 4 (SIQ, ISQ) just don't match the pattern from above—they mess up the consistent +4 and -4 jumps we've seen.

If you’re looking for the underlying method, it’s a classic pattern of increasing/decreasing by fixed steps in the alphabet for each letter position. Simple, recognizable, and a little satisfying once you spot it.