Answer:
A)They most likely used an experiment with students randomly assigned to watch more than one hour or less than one hour of TV each night.
Explanation:
For the study, the likely design to have been used is the experimental.
It would be expected that random selection of students would be made, and they would be assigned to the two groups - those who watch more than one hour of TV each night and those who watch less than one hour. Their initial weights measured, and the study is for a period of time.
After the period, the weight of each student is remeasured and compared to their initial weight. Then the conclusion can be made.
Thus, they most likely used an experiment with students randomly assigned to watch more than one hour or less than one hour of TV each night.