Concept:Sentence rearrangement based on logical flow and grammatical connectors.
Explanation:The first part is P because it introduces a general idea about the temperature of a layer.
P ends with "layer of the", which links directly to "atmosphere" in S — so S follows P.
S ends with "we must be careful", and Q begins with "when", which modifies that caution — so Q follows S.
Finally, R ("measurements of temperature") completes the thought started in Q ("directly comparing the satellite ...").
Thus the correct order is P → S → Q → R.
Answer:Option (2): P S Q R