Five students — A, B, C, D, E — sit in a row. A must sit next to B. C cannot sit next to D. How many valid arrangements are there?

✓ Correct Answer: Option B

Treat AB as a unit (2 internal arrangements). 4 units in a row = 4! = 24. Subtract C-next-to-D cases. With AB as a unit, there are 12 arrangements where C is next to D. So 48 - 12 = 36.