In the letter series, some of the letters are missing, which are given in the alternatives (A), (B), (C) and (D).
m n o n o p q o p q r _ _ _ _ s t u

(A) r
(B) s
(C) q
(D) p

Choose the correct sequence from the options given below:

(B), (D), (C), (A)

The correct answer is Option (4) → (B), (D), (C), (A)

Step-by-step observation

The series is formed by overlapping alphabetic sequences, each time:

• the starting letter shifts forward by one, and
• the length of the sequence increases by one.

So we get:

1. m n o → 3 letters
2. n o p q → 4 letters
3. o p q r s → 5 letters
4. p q r s t u → 6 letters

Now compare this with the given sequence:

After o p q r, the next four missing letters should be:

p, q, r, s

Match with options

Missing letters in order:

• p → (D)
• q → (C)
• r → (A)
• s → (B)

But the question asks for the correct sequence of options, so the order is:

(B), (D), (C), (A)