Query about Question 1 from "Timed Quant Practice - Hard Section 2 Sample Test #5" [9174]

GRE GRE Quant Problem Solving
1

https://www.gregmat.com/quizzes/quiz/timed-quant-practice-hard-section-2-sample-test-5 (Question 1)

Where in the question is it mentioned that “sets are not allowed to have duplicate elements” ?

2

Refer to Sets versus Lists - PrepSwift