The sentence 'Then it struck me how eminently suitable it was of course' makes grammatical sense and conveys a complete thought. The PSRQ arrangement creates a coherent sentence where the speaker realizes something is suitable. Option A (SPQR) places 'how eminently' before 'it struck me', which is awkward. Option B (QSRP) and D (QPSR) create nonsensical word orders that don't form proper English sentences.