Concept:Rearranging jumbled sentence parts to form a logical sequence.Explanation:Identify the first part: 'S' introduces the subject "gain sharing-plans" independently.'P' follows as it describes what these plans do ("are now used by more than a thousand firms").'R' logically comes next because it specifies the location ("in the United States and Europe") linked to "firms".'Q' concludes by adding that the plans "are growing in popularity".Thus the correct order is S, P, R, Q.Answer:Option D: S P R Q