A study examined the effect of garlic on blood cholesterol levels. A total of 192 subjects with starting LDL ("bad cholesterol") levels between 130 and 190 mg/dl were randomly assigned to one of the 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 of the following principles of experiments was used in this study?

A) Randomization
B) Blinding
C) Blocking
D) All of these answers are correct