As the solar nebula collapsed, it became a disk becausea) the overall rotation of the nebula plus collisions between particles made the particles go in more or less the same direction. b) the initial cloud was disk shaped. c) the sun's gravity pulled the nebula material into the ecliptic plane. d) the self-gravity of the nebula pulled the material into the ecliptic plane.

a) the overall rotation of the nebula plus collisions between particles made the particles go in more or less the same direction

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.