Concept:Identifying the logical flow of a sentence by arranging its jumbled parts.
Explanation:Start with segment Q: it introduces the main topic, "a final problem is that the tendency towards".
Segment P follows naturally: it specifies what the tendency is—"moderation and compromise may mean that multiparty".
Segment S continues the thought: "systems are so dominated by the political centre that they".
Segment R completes the sentence: "are unable to offer clear ideological alternatives".
Thus, the correct order is Q, P, S, R.
Answer:QPSR (Option B).