A Researcher Is Interested in Investigating the Relationship Between Sugar

A researcher is interested in investigating the relationship between sugar consumption and weight gain for high school students. Fifteen volunteers were randomly assigned to one of two groups. The first group contained six volunteers who were put on a low-sugar diet. The second group consisted of the remaining nine volunteers, who were put on a diet in which sugar constituted approximately 15% of their calories consumed. After eight weeks, the change in weight was recorded for each of the volunteers.
What is the response variable in this study?

A) Percent of sugar in the diet
B) Eight-week time period
C) Assignment to groups
D) Change in weight