Select all that apply. quarks are thought to be the basic component of protons electrons neutrons

Quarks are types of particles and a basic constituent of matter. They form composite particles called hadrons when they combine. 
They are fundamental components of Protons and neutrons.

protons and neutrons.

Justification:

Contrary to the belief of some years ago, protons and neutrons are not considered elementary or fundamental particles any more. 

Electrons remain being considered elementary particles.

All three, protons, electrons and neutrons are subatomic partilces, but the only elemental particle of them is the electron.

That means that protons and neutrons are composite particles (they are composed by other smaller, elementary particles).

Those particles that constitute the protons and neutrons are the quarks, as stated by the question.