Answer:
a) the overall rotation of the nebula plus collisions between particles made the particles go in more or less the same direction
Step-by-step explanation:
According to the solar nebula the formation of the solar system began with the collapse of the molecular hydrogen—giant molecular clouds.
The collapse was accompanied by a certain amount of angular momentum. As the rotating mass gains momentum by the addition of mass a disc is formed. This rotating mass begins the formation of the protostar. The protostar is the initial stage of the star which is forming from the parent molecular cloud.