P : the morning session lasting three hours, was spent Q : mainly on reviewing R : in the fourth round of talks S : the implementation of the decisions taken The Proper sequence should be:

The correct answer is: A. PQRS

The morning session lasting three hours was spent mainly on reviewing the implementation of the decisions taken in the fourth round of talks.

Option B, PQSR, is incorrect because the implementation of the decisions taken should come after reviewing them.

Option C, PRQS, is incorrect because the fourth round of talks should come after the implementation of the decisions taken.

Option D, PRSQ, is incorrect because the morning session lasting three hours should come before reviewing the implementation of the decisions taken.