To determine the proper order of the sentences, we need to logically connect each sentence based on the context provided by the first and sixth sentences. Let's analyze the sequence:
1. S1 states that all the land was initially covered by the ocean.
2. Q introduces the problem: a terrible monster preventing the gods from separating the land from the water, establishing a conflict.
3. P describes how the leading god resolved the conflict by fighting and killing the monster, splitting its body into two halves.
4. R explains the creation of the sky using the upper part of the monster's body, embellished with stars, showing a progression in creation.
5. S details the formation of the earth from the lower part of the monster's body, complete with plants and animals, continuing the creation narrative.
6. S6 concludes with the creation of humans, molded from clay, according to the god's image and mind.
The logical sequence that fits this progression is: QPRS, matching the correct answer choice.