Question

which object(s) formed last in our solar system? the sun the solar nebula the inner planets the planetesimals

Explanation:

The solar nebula was the initial cloud - like mass from which the Sun and solar system formed. The Sun formed first from the densest part of the nebula. The inner planets formed from the accretion of planetesimals. Planetesimals are small bodies that aggregated to form planets. So the inner planets formed after the planetesimals aggregated.

Answer:

the inner planets