As an assignment for her Psychology class in College, Elena is conducting an experiment to determine if high school students are more relaxed when the lights are off or when music is played during an exam. She selects 10 of her friends to take an exam with the lights off and another 10 of her friends to take an exam with music playing What is problematic about the way that Elena selected her groups?

a) There is nothing wrong with how Elena selected her groups.

b) Elena should have selected the first 20 students from the local high school that she ran into at the mall.

c) Elena did not select students at random from a typical high school

d) Elena did not have to select high school students.

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