(which is sold) P (for its horn) Q (the Rhinoceros is hunted by poachers) R (at high prices) S The correct sequence should be

Since, the starting statement carries a subject; R will be the first statement. The next statement describes why are they hunted, so Q follows P, as it states that what is being done with the horns. S would be the concluding statement and thus form a coherent paragraph.

The correct formation would be, ‘The Rhinoceros is hunted by poachers for its horn which is sold at high prices.’