Concept:The correct sequence of sentences (P, Q, R, S) between S1 and S6 is determined by logical flow of ideas about idioms.
Explanation:S1 introduces idioms as a colourful aspect of language.
Q logically follows: it states idioms are commonly used in all language types.
Next, P explains that understanding idioms improves language skills.
Then, S highlights a key problem: idiom meanings are often not guessable from the words.
After that, R adds that idioms have a stronger meaning than non‑idiomatic phrases.
Finally, S6 concludes by noting that idioms can reveal the user's attitude.
Thus the correct order is S1 → Q → P → S → R → S6.
Answer:The correct sequence is QPSR, which corresponds to option D.