1. what is a neutron star left over from?\na planetary nebula\na black hole\na supernova\na white dwarf

Brief Explanations:

A neutron star is formed when a massive star undergoes a supernova explosion. The core of the star collapses under its own gravity, and if the mass of the core is between about 1.4 and 3 solar masses, it forms a neutron star. Planetary nebulae are the remnants of low - to medium - mass stars, black holes form from more massive core collapses, and white dwarfs are the remnants of low - to medium - mass stars that have exhausted their nuclear fuel without going supernova.

Answer:

C. a supernova