Question

where do planets form in interstellar nebulae?
a planetary nebula
b interstellar space
c protoplanetary disk
d protostar

Explanation:

Planets form in protoplanetary disks within interstellar nebulae. These disks are made of gas and dust around a young star (protostar). Planetary nebulae are the remnants of dying stars and not where planets form. Interstellar space is too diffuse for planet - formation. A protostar is the early stage of a star, not the location of planet - formation.

Answer:

C. protoplanetary disk