Explanation:

Let's break down the pattern:

- Split each cluster into two parts: first two and last two letters.

- Look at positions in the alphabet:

K(11), M(13), T(20), C(3)

E(5), V(22), O(15), M(13)

O(15), Q(17), X(24), G(7)

I(9), Z(26), S(19), Q(17)

Let's analyze how each letter moves in the series:

- 1st letters: K, E, O, I

• K(11) ? E(5) (–6), E(5) ? O(15) (+10), O(15) ? I(9) (–6)

• Pattern: –6, +10, –6, ... next should be +10 ? I(9) + 10 = S(19)

- 2nd letters: M, V, Q, Z

• M(13) ? V(22) (+9), V(22) ? Q(17) (–5), Q(17) ? Z(26) (+9)

• Pattern: +9, –5, +9, ... next should be –5 ? Z(26) – 5 = U(21)

- 3rd letters: T, O, X, S

• T(20) ? O(15) (–5), O(15) ? X(24) (+9), X(24) ? S(19) (–5)

• Pattern: –5, +9, –5, ... next should be +9 ? S(19) + 9 = B(28) (as the alphabet only has 26 letters, B(2))

- 4th letters: C, M, G, Q

• C(3) ? M(13) (+10), M(13) ? G(7) (–6), G(7) ? Q(17) (+10)

• Pattern: +10, –6, +10, ... next should be –6 ? Q(17) – 6 = K(11)

Putting it all together: S U B K

Options:

- 1. SUCL

- 2. SVCK

- 3. TVBK

- 4. SUBK

Correct Answer: Option 4 - SUBK

Explanation in bullets:

- The sequence alternates between adding and subtracting set values to each letter.

- The first letters follow the pattern –6, +10 alternately.

- The second letters follow +9, –5 alternately.

- The third letters follow –5, +9 alternately, using alphabet wrap-around if needed.

- The fourth letters follow +10, –6 alternately.

- Tracking the position yields S U B K for the missing cluster.

- Option 4 matches: SUBK