How long was one city block in Chicago in 1871

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.

Hurry ! between 1900 and 2010, how did the world’s population change? a. it increased from about 1.5 billion to almost 7 billion. b. it decreased from about 7 billion to about 1 billion. c. it increased from about 5 billion to about 7 billion. d. it decreased from about 7 billion to about 1.5 billion.

Which of the following contributed most to making the items listed in the box