Answer:
Intervention study
Step-by-step explanation:
An intervention study is a type of controlled clinical trial in which an intervention is applied to a group of people and the outcome is compared to a similar group without the intervention. An example of this type of study is shown in the question above, where a margarine which vegetable ingredients (which is the intervention) will be given to a group of people, so that their blood cholesterol levels are compared to the cholesterol levels of a group of people who didn't use this margarine.