Which of the following statements is true about immigrants in the united states?
a. the majority of immigrants to the united states have come from africa.
b. all immigrants to the united states have come from europe.
c. everyone in the united states, with the exception of native americans, is an immigrant or a descendent of an immigrant.
d. few people in the united states today are descendents of immigrants.

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.