The graph below shows the number of cars purchased in selected years between 1910 and 1926. Which was MOST LIKELY to have been an incentive for the trend seen in the graph?
A. The price of cars decreased during this period.
B. The later cars were made out of more expensive materials
C. Restrictions were placed on the type of fuel cars used.
D. The government restricted the number of cars that could be produced in a given year

The authors of the paper "fudging the numbers: distributing chocolate influences student evaluations of an undergraduate course"† carried out a study to see if events unrelated to an undergraduate course could affect student evaluations. students enrolled in statistics courses taught by the same instructor participated in the study. all students attended the same lectures and one of six discussion sections that met once a week. at the end of the course, the researchers chose three of the discussion sections to be the "chocolate group." students in these three sections were offered chocolate prior to having them fill out course evaluations. students in the other three sections were not offered chocolate. the researchers concluded that "overall, students offered chocolate gave more positive evaluations than students not offered chocolate." indicate whether the study is an observational study or an experiment. give a brief explanation for your choice.