Question

1. what is the main force that causes a protostar to become a star?

Explanation:

A protostar forms from a collapsing cloud of gas and dust. The main force causing it to become a star is gravity, which pulls matter inward, increasing pressure and temperature at the core until nuclear fusion starts.

Answer:

Gravity (the gravitational force pulls the matter of the protostar inward, increasing core pressure and temperature until nuclear fusion initiates, transforming it into a star)