a professor wants to determine whether her students perform better on mid-term examinations if they write their exam alone or in a group. the professor believes that students who write the exam in private cubicles will score lower than the students who write in their regular classroom. to experimentally investigate this possibility, she randomly assigns half of her students to write their mid-term in the regular class setting and randomly assigns the other half of her students to write their mid-term individually in private cubicles in the university's testing centre. which of these conditions is the experimental group?