Answer:
B. Randomly assigning students to the two different groups
Explanation:
The bias can be controlled by making use of the randomized block design where we divide the subject into subgroups also called blocks and randomly assign treatment conditions to each block.
In this case, the blocks or sub groups are learning math from a video game and learning it from traditional classroom activities.
So the best way to control the bias is by randomly assigning students to the different groups.
