What comes next? CBA, DCB, EDC, FED, ?

Correct — B.
Rule: each term is three consecutive letters written backwards, and the first letter moves +1.

First letters: C, D, E, F → G.
Written backwards from G: G, F, E → GFE, option (b).

Why the others are wrong

• (a)
  HGF — HGF starts at H, skipping G. The first letters run C, D, E, F, so the next term must start at G.
• (c)
  GEF — GEF has the right letters in the wrong order. Every term runs backwards, so G must be followed by F, then E.
• (d)
  FGE — FGE starts with F again, repeating the first letter of FED, and it breaks the backward order.

In a letter-cluster series, read each position as its own series, column by column. First letters: C, D, E, F. Second letters: B, C, D, E. Third letters: A, B, C, D.

Each column moves +1, so the next term is G, F, E. Seen whole, every term is three consecutive letters written backwards.

Key facts

• In CBA, DCB, EDC, FED, GFE each column moves +1.
• Each term is three consecutive letters in reverse order.
• FED is followed by GFE, not HGF.

Common traps

• Picking GEF because it has the right three letters, ignoring their order
• Jumping to HGF by moving the first letter two steps instead of one

No directly related past PYQ was found.