Answer : Option D) The He quarks
Explanation :
The scientist uses an accelerator and high energy electrons to study the particles inside the protons of a helium atom, the particles under study are quarks.
Quarks are the elementary and fundamental part of matter. In Helium nucleus when the high energy is bombarded to study the particles inside the proton it is obvious that the scientist is studying the quarks inside the proton. In a proton there are two up quarks and one down quark present.