Identify the sampling method​ (simple random​ sampling, systematic​ sampling, convenience​ sampling, cluster​ sampling, or stratified​ sampling) in the following study. Researchers studying the use of anabolic steroids select 61 participants between the ages of 20 and​ 29, 61 participants between the ages of 30 and​ 39, and 61 participants between the ages of 40 and 49.
a) Stratified sampling
b) Convenience sampling
c) Cluster sampling
d) Systematic sampling
e) Simple random sampling