Please help me please please please​

Chris would like to conduct a study on the effectiveness of a new substance-abuse treatment program. he has a sample of participants go through the program and he uses as a comparison group people who did not volunteer for the program but were eligible. chris has used a(n) design for his study.

Why do governments supply public goods and services instead of selling them to those people who use them

Which article of the us constitution addresses the issue of interpeting the laws of the united states