The answer is:
B) The number of students who smoked electronic cigarettes increased slowly between 2011 and 2016.
According to the excerpt from "Youth and Tobacco Use," the number of middle school students who smoked electronic cigarettes had a low increment of 0.6% in 2011. At the same time, the percentage of high school students raised 1.5% during the same period.
The rest of the alternatives are incorrect because they do not express the main or the entire purpose of the paragraph.