Why Might Inflation Have Occurred at the End of the GUT

Why might inflation have occurred at the end of the GUT era?

A) Gravity was an extremely weak force at this period in time.
B) Large amounts of matter and antimatter annihilated at this time.
C) There wasn't enough matter present to slow down the expansion at that time.
D) The universe was too small and needed to grow quickly.
E) An enormous amount of energy was released when the strong force froze out from the GUT force.