Question

Which sentence contains correct parallel structure?

Answer 1

Answer:

He wanted three things out of the class: to learn a new skill, to make new friends, and to develop a different mindset.

Explanation:

Three infinitives (to learn, to make, to develop) explain the object three things; that's parallelism, i.e. use of identical grammatical construction.

The other options use both gerund(s) and infinitive(s). Using different constructions cannot create parallelism; that's why  those sentences do not contain correct parallel structure.