A Study Examined the Effect of Garlic on Blood Cholesterol

A study examined the effect of garlic on blood cholesterol levels. A total of 192 subjects with starting low-density lipoprotein (LDL) cholesterol ("bad cholesterol") levels between 130 and 190 mg/dl were randomly assigned to one of four treatments for six months: raw garlic eaten daily, a powdered garlic supplement taken daily (Garlicin brand) , an aged-garlic extract taken daily (Kyolic brand) , or a placebo pill taken daily. The study found no significant or clinical differences in blood cholesterol levels between the four groups at the end of the study.
Which type of study is this?

A) Stratified comparative survey
B) Completely randomized experiment
C) Matched pairs experiment
D) Stratified experiment