S could go either third or forth - this is a could be true question, so the correct answer is only one of possible scenarios. If G performs first, we know that R&S must also perform before T. H must perform earlier than R, so H must also perform earlier than T. H must perform either earlier than both S & T or later than both of them, we know that H cannot perform later than T, hence it must perform earlier than both S & T. We can conclude that overall the order of the students must be:

G H S/R S/R T

As you can see (E) is impossible, because T must always go fifth if G goes first.

Let me know if this makes sense and if you have any further questions.