The correct answer is D. SRPQ.
The first sentence (S1) states that patients with speech disorders can think without having adequate control over their language. The second sentence (P) provides an example of this, saying that some patients fail to find the names of objects presented to them. The third sentence (R) further supports this claim, saying that patients can use concepts needed for chess playing even though they are unable to express many of these concepts in ordinary language. The fourth sentence (S) provides another example of this, saying that patients find it difficult to interpret long written notices. The sixth sentence (S6) concludes by saying that we do not know how patients manage to do this.
The other options are incorrect because they do not follow the logical order of the sentences. For example, option A (PSQR) puts the sentence about chess playing (R) before the sentence about object naming (P). This is not logical because the sentence about object naming provides an example of the claim made in the first sentence, while the sentence about chess playing provides an example of the claim made in the third sentence. Option B (QSPR) puts the sentence about object naming (Q) before the sentence about chess playing (R). This is also not logical because the sentence about object naming provides an example of the claim made in the first sentence, while the sentence about chess playing provides an example of the claim made in the third sentence. Option C (RPSQ) puts the sentence about chess playing (R) before the sentence about object naming (P) and the sentence about long written notices (S). This is not logical because the sentence about object naming provides an example of the claim made in the first sentence, while the sentence about chess playing provides an example of the claim made in the third sentence. The sentence about long written notices is not relevant to the main argument of the paragraph, which is that patients with speech disorders can think without having adequate control over their language.