What comes next? MZM, PXK, SVI, ?

Correct — A.
Rule: each position moves by its own step: first letter +3, second −2, third −2.

First: M → P → S → V (+3)
Second: Z → X → V → T (−2)
Third: M → K → I → G (−2)
Next term: VTG → option (a)

Why the others are wrong

• (b)
  USF — USF gets every letter wrong: U is S + 2 (the step is +3, giving V), S is V − 3 (the step is −2, giving T), and F is I − 3 (should be G).
• (c)
  WTG — WTG has the right second and third letters, but W is S + 4. The first letters rise by exactly 3 (M, P, S), so the next is V.
• (d)
  XRE — XRE overshoots every position: X is S + 5, R is V − 4 and E is I − 4, against steps of +3, −2 and −2.

In a letter-cluster series, read the clusters column by column, not word by word. Each position is a separate series with its own step.

Convert letters to alphabet positions to see the steps: M 13, P 16, S 19 (+3); Z 26, X 24, V 22 (−2); M 13, K 11, I 9 (−2).

Then extend each column by one step: V 22, T 20, G 7.

Key facts

• Alphabet positions used here: G 7, I 9, K 11, M 13, P 16, S 19, T 20, V 22, X 24, Z 26.
• In a letter-cluster series each position can follow a different step, so solve one column at a time.
• Here two of the three columns move backwards: Z → X → V and M → K → I.

Common traps

• Reading each cluster as a word and hunting for a pattern inside it, instead of down the columns.
• Counting M → P as +2 by counting the letters in between (N, O) rather than the positions, 13 to 16.

No directly related past PYQ was found.