Which sentence contains correct parallel structure?

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

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

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

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