Step 1: Start from S1 and look for a definition-expansion.
S1 gives a general statement about a library. A natural continuation is to specify what it contains. Sentence Q does exactly this by listing “books, journals, and digital resources.”
\( \Rightarrow \) \(\underline{Q}\) should come immediately after S1.
Step 2: Resolve the anaphora “these resources.”
Sentence S mentions “these resources,” which must refer to something introduced earlier. Only Q introduces resources explicitly, so S must follow Q.
\( \Rightarrow \) partial order: S1 \(\to\) Q \(\to\) \(\underline{S}.\)
Step 3: Bring in the users, then the effect on them.
After resources and their management (Q, S), the next logical idea is who uses them. Sentence P introduces “Students and researchers … visit to find useful information,” which connects naturally to the resources.
Sentence R talks about “visitors” focusing due to the peaceful environment—this refers back to the visitors in P, so R must follow P.
\( \Rightarrow \) order of the middle four becomes: Q \(\to\) S \(\to\) P \(\to\) R.
Step 4: Conclude with S6.
With contents (Q), management (S), users (P), and environment (R) established, S6’s “Thus” provides a coherent summary.
\(\boxed{\text{Proper sequence of the four sentences: QSPR}}\)