Daily Chess Improvement: Spot the right plan!

This is based on another similar chess puzzle I created for SPFGI

White to move. How should white proceed?

  1. Qxb8+!!

a) 1...Kd7, 2. Nc5+ Ke7, 3. Qxc7+ Bd7 (forced), 4. Qxd7#

b) 1...Kxb8, 2. Nc5! (threatening 3. Rhb3+ and 4. Ra8#) Kc8, 3. Ra8#