Concept:Logical sequencing of sentences to form a coherent narrative based on cause and effect.
Explanation:R begins the sequence: "He had begun to write, when he remembered..." – this sets the situation and the problem (missing papers).
Q follows naturally: "He lifted the receiver, dialed..." – he takes action to solve the problem by calling Cartwright.
P comes next: "Could Cartwright possibly find a messenger..." – this is a question arising from the call, asking for help.
S concludes: "He would be very grateful" – an expression of thanks, logically ending the exchange.
Other options do not maintain this logical flow. For example, placing P before R would break the sequence of events.
Answer:The correct sequence is RQPS, which corresponds to option A.