Determine whether each of the following studies is an experiment or an observational study.

(a) A medical researcher is going to study the relationship between cell phone use and Alzheimer’s disease.

(b) A medical researcher is going to study the relationship between recovery time after heart bypass surgery and age.

(c) A fertility clinic is going to study the optimal temperature in which to store frozen sperm.

(d) A medical researcher at a pharmaceutical lab has developed a new synthetic antibiotic and needs to determine the appropriate dosage of this antibiotic.