Step-by-step Solution:

Pattern Analysis

The series follows two distinct patterns working together:

• 
  Length Pattern: Each term in the series increases in length by one letter.
  
  A (1 letter), CD (2 letters), GHI (3 letters), ? (must be 4 letters), UVWXY (5 letters).
  


• 
  Gap Pattern: The number of letters skipped between terms is equal to the length of the preceding term.
  
  
  
  • After A (length 1), skip 1 letter (B). Next term starts with C.
  
  
  • After CD (length 2), skip 2 letters (E, F). Next term starts with G.
  
  
  • Therefore, after GHI (length 3), we must skip 3 letters (J, K, L). The next term must start with M.
  
  
  
  

By combining these two patterns, the missing term must start with the letter M and be 4 letters long.

The correct answer is B. MNOP