What Event Occurs at the End of the Protostar Stage

Multiple Choice

What event occurs at the end of the protostar stage of a star's life?

A) Nuclear reactions begin in its core,converting hydrogen into helium,generating energy and increasing internal pressure.
B) It explodes,forming a supernova remnant.
C) It begins a long period of contraction,in which gravitational energy is converted into heat.
D) Gas is spun off from its equator,forming planets.