Randomized controlled trials are which type of research?

The correct answer to this open question is the following.

Randomized controlled trials are considered to be the gold standard of study design because they determine casualty, to approximate a controlled experiment, to reduce bias and confounding variables and because it is statistically efficient.

A randomized controlled trial is the kind of study that randomly chooses the participants in a group that is controlled. The outcome of the variable of the study is the expected difference in the study.