The question below consists of a set of labelled sentences. Out of the four options given, select the most logical order of the sentences to form a coherent paragraph.

P. Thus, that waste can be used to refill the pit.

Q. In many cases, a fairly large quantity of overburden or waste is excavated which does not contain many minerals.

R. Mining can alter any landscape drastically.

S. But it is costly to re-excavate it and refill the pit.