A class consists of six students: P, Q, R, S, T, and U. The selection criteria are: 1) P cannot be selected if Q is selected. 2) R must be selected if S is selected. 3) T can be selected only if U is not selected. Which of the following combinations is valid?

Answer: C. R, S, T
R and S can be selected together, and T can be selected independently of U.