Key changes observed during the upper paleolithic (from about 40,000 to 10,000 years ago) include all of the following except
a) increased sophistication of tools.
b) expansion of the human geographic range.
c) domestication of most plant and animal foods.
d) the invention of new equipment, such as bows and arrows.
all of the above occurred between 40,000 and 10,000 years ago.

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.