A Researcher Is Conducting an Experiment Over a School Year

A researcher is conducting an experiment over a school year to determine if a drug prevention program is working amongst high school juniors and seniors.They ask students about their drug use habits at the beginning of the school year,and then again after the program ends.Additionally,another demographically similar school that is not using the program is given the same surveys to compare.All of the students had to voluntarily participate in the program.What is not being controlled for/

A) selection biases.
B) testing.
C) history.
D) maturation.
E) causal time-order