Explanation:

Let's break down how the sequence works:

- Take the first letters: W, U, S, ?. Each time, the letter goes back by two—W (23rd), U (21st), S (19th), so the next should be Q (17th).

- Now the second letters: F, C, Z, ?. F (6th), C (3rd), Z (26th), the pattern is -3, -3, -3, but after Z comes W (23rd, since after going back by three from Z: Z ? W).

- Next, B, W, R, ?. B (2nd), W (23rd), R (18th), pattern is -5, -5, which means after R (18th), subtract 5 gives N (13th).

- Last letters: I, B, U, ?. I (9th), B (2nd), U (21st), let’s see the jump: 9 ? 2 (-7), 2 ? 21 (+19, but actually, in alphabet cycles it's +19, which is weird but let's keep going). If we keep the move of adding 19 when wrapping around: U(21) + 19=40, modulo 26 equals 14, which is N.

- Checking all the given options:

1. QWMN

2. QXNN

3. QWNN

4. QXMN

- Matching our work: First: Q, second: W, third: N, last: N.

- So, QWNN is the fit.

And the correct answer is:

- Option 3: QWNN

Here's what it boils down to:

- The pattern for each letter goes back by regular jumps.

- Option 3 is the only one that fits all four places for letter positions.

- Option 1 (QWMN) looks close but misses with the third letter (it should be N, not M).

- Option 2 and 4 mess up the second letter—should be W, not X.

Hope that clears it up!