Answer:
(B) An uncontrolled experiment.
Step-by-step explanation:
In the case of an uncontrolled experiment here all participants are provided the similar treatment and there should be no comparison oppose to any group i.e. controlled
Since in the given situation, there are similar diets are provided to 20 volunteers and it can be that the cholesterol level is decreased after particular time period,
Hence, it is an uncontrolled experiment.
Thus, option B is correct.
