Sentence improvement (modal perfect and adverb placement): verify that the sentence is already correct Original sentence: "They should have calmly thought of the advantages that would accrue to them." Decide whether a correction is needed; if not, select “No correction required.”

Why the original is correct
The structure should have + past participle (should have thought) correctly expresses a past advisability. The adverb “calmly” is well placed before the main verb (thought). The phrasal verb “think of (the advantages)” is standard, and “that would accrue to them” is a correct relative clause.

Option analysis (errors)
should have been calm in thinking about — clumsy and changes the predicate structure.should be calmly thought of — passive; changes the subject and meaning.shall have to calmly thought of — tense/aspect errors and ungrammatical form after “to”.should have calmly think of — wrong form; needs past participle “thought”.

Final Answer
No correction required