What Caused the Late Heavy Bombardment in Our Solar System

Multiple Choice

What caused the Late Heavy Bombardment in our solar system?

A) Debris from the impact that formed the Moon scattered throughout the inner solar system.
B) The changing orbits of the giant planets disturbed the orbits of many asteroids.
C) The close passage of Scholz's star disturbed the orbits of bodies in the Oort cloud and Kuiper belt.
D) Gravitational resonances between Neptune and Kuiper belt objects caused many of the latter to collide with the inner planets.