Answer: 
The correct answer would be A) DNA. 
Electrophoresis or gel electrophoresis is a technique used to separate the charged particles such as DNA, RNA, and proteins on the basis of their size. 
Under this technique, the charged particles are allowed to move under a uniform electric field. 
The gel or gel pores act as a sieve through which the charged particles move and thus, the smallest fragment reaches the farthest end and in the smallest interval of time. 
For example, DNA is a negatively charged particle which moves from cathode to anode and DNA fragments are separated according to their size.