To learn about the TV viewing habits of all the children attending Oakbridge School, Professor DeVries randomly selected and interviewed 50 of the school's students. In this instance, all the children attending the school are considered to be a(n):.
a. control condition.
b. representative sample.
c. independent variable.
d. population.

A population-D

Explanation:

A population is referred to  a large collection of individuals or objects that is the main focus of an experiment or scientific research query. It is also called A research population because it considers a defined collection of individuals or objects who have similar binding  characteristics.

Professor DeVries randomly selected and interviewed 50 of the school's students of Oakbridge School. He is using a well defined collection of student with same characteristic ie same school . His study is using a Population. Note that "random"  here implies a subset of a population.  

b. the american revolution