Answer:
C. protostar
Step-by-step explanation:
Due to the effect of gravity the hydrogen atoms are pulled together from the nebula. At this stage the star is not hot enough to start the nuclear fission. At this stage a star is called protostar. Eventually it will grow in size by attracting more hydrogen. When the temperature at the core is increased enough due to the gravitational pressure at the core of the star, then nuclear fission will start