Medical researchers studying the effects of a low carb diet versus a normal diet randomly assigned obese patients to one of the two diets. The patients were followed up with after several months and the amount of weight lost (lbs) was recorded. Researchers advised against interpreting these results as a universal endorsement of low-carb diets for the general population wanting to lose weight. Why would the researchers give this advice? (Choose the most appropriate answer).

A.This experiment did not use blinding.

B.This experiment only used obese subjects.

C.This is an observational study so we cannot establish that the low-carb diet causes weight loss.