An investigator reviewed the medical records of 200 children seen for care at boston medical center in the past year who were between the ages 8 and 12 and identified 40 children with asthma. he also identified 40 children of the same ages who were free of asthma. each child and their family were interviewed to assess whether there might be an association between certain environmental factors such as exposure to second-hand smoke. this study is an example of a: a. randomized controlled trial. b. case-control study. c. cohort study. d. crossover trial.

cohort study

Step-by-step explanation:

Given that an  investigator reviewed the medical records of 200 children seen for care at Boston Medical Center in the past year who were between the ages 8 and 12 and identified 40 children with asthma. He also identified 40 children of the same ages who were free of asthma. Each child and their family were interviewed to assess whether there might be an association between certain environmental factors such as exposure to second-hand smoke.

The objective of this experiment is to test the causes of the disease asthma and to find the risk factors and environment causing this disease.

So this cannot come under randomized control nor case control.

Cross over study is to put to two different environments two groups and study.  But here nothing is influenced actual environments are studied

Hence this comes under cohort study

is means division by fractions

step-by-step explanation: