Question

what must occur for a protostar to become a main sequence star? it must eject its surrounding dust it must begin hydrogen fusion in its core it must form a planetary system it must rotate quickly

Explanation:

A protostar becomes a main - sequence star when nuclear fusion (specifically hydrogen fusion) starts in its core. This fusion process provides the energy to balance the gravitational forces within the star, stabilizing it. Ejecting surrounding dust is part of the protostar formation process but not the key to becoming a main - sequence star. Forming a planetary system is an event that may occur around a star but is not a requirement for a protostar to become a main - sequence star. Rotation speed is not the determining factor for a protostar to transition to a main - sequence star.

Answer:

It must begin hydrogen fusion in its core.