Final answer:
The material in the asteroid belt did not form into a planet due to Jupiter's disruptive gravity and the insufficient amount of material.
Step-by-step explanation:
The reason the material in the asteroid belt did not form into a planet like the other planets is option d - the gravity of Jupiter disrupted the formation process. Astronomers hypothesize that Jupiter's gravitational perturbations could have dislodged the orbits of rocky planets in the asteroid belt, causing them to fall into the Sun. This idea is consistent with the fact that Uranus and Neptune likely formed closer to where Jupiter and Saturn are now. Additionally, the asteroid belt contains insufficient material to form a planet like Jupiter or Saturn.