Question

a t tauri star is a new star that has just initiated nuclear fusion and joined the main sequence. type of variable star with a direct relationship between period and luminosity that can be used to determine distances. protostar that is just emerging from the cloud of dust and gas it formed within. star that has exhausted the supply of hydrogen in its core and grown large, cool, and bright.

Explanation:

A T - Tauri star is a young, pre - main - sequence star. It is a protostar that has not yet begun stable hydrogen fusion in its core and is emerging from the molecular cloud of dust and gas from which it formed. Stars that have initiated nuclear fusion and joined the main sequence are main - sequence stars. Cepheid variables have a direct relationship between period and luminosity for distance determination. Stars that have exhausted hydrogen in their core and grown large, cool, and bright are red giants.

Answer:

C. protostar that is just emerging from the cloud of dust and gas it formed within.