Which One of the Following Instances Is MOST Like a Random

Which one of the following instances is MOST like a random sample for a class of thirty students?

A) A coin is tossed in order to select students alternately one by one into the experimental and control groups.
B) The first ten students who enter the classroom are placed into the experimental group and the next ten into the control group.
C) The first twenty volunteers are selected from the physics class and alternately placed into experimental and control groups.
D) The twenty students with the highest GPAs are selected and alternately placed into experimental and control groups.