Which shows the correct order of processes leading up to the formation of a main sequence star? a. gases condense to form a nebula, gravity causes the nebula to collapse and spin, nuclear fusion occurs, and a protostar forms. b. a protostar forms, nuclear fusion occurs, gases condense to form a nebula, and gravity causes the nebula to collapse and spin. c. gases condense to form a nebula, gravity causes the nebula to collapse and spin, a protostar forms, and nuclear fusion occurs. d. a protostar forms, gases condense to form a nebula, gravity causes the nebula to collapse and spin, and nuclear fusion occurs.