TMUA 2019 Paper 2 Question 12

Most students in a large college study Mathematics. A teacher chooses three different students at random, one after the other. Consider these three probabilities: $$R=P(\text{at least one of the students chosen studies Mathematics}),$$ $$S=P(\text{the second student chosen studies Mathematics}),$$ $$T=P(\text{all three of the students chosen study Mathematics}).$$ Which of the following is true?