What Finally Halts the Core Collapse in the Initial Stages

Multiple Choice

What finally halts the core collapse in the initial stages of the formation of a Type II supernova?

A) The core becomes a singularity, with all matter concentrated at a single point.
B) The iron core stiffens when it reaches the density of nuclear matter, producing the core bounce.
C) The iron core becomes hot enough to begin fusion reactions, which produce a uranium core.
D) The temperature becomes great enough to produce radioactive nuclei.