参考答案：A

解析： 29-31
(29) The manager of a large office building had received many complaints about the lift service in the building. The engaged a group of engineers to study the situation and make recommendations for improvement. The engineers suggested two alternative solutions: 1 ) adding more lifts of the same type; 2) replacing the existing lifts by faster ones.
(31) The manager decided that both alternative solutions were too expensive. So the firm’s psychologist offered to study the problem. He noticed that many people arrived at their offices feeling angry and impatient. The reason they gave was the length of time they had to wait for the lift. However, the psychologist was impressed by the fact that they had only had to wait a relatively short time. (30) It occurred to him that the main reason for their annoyance was the fact that they had to stand by the lifts inactive. He suggested a simple, inexpensive solution to the manager. That is, to place a large mirror next to the lifts.
29. What did the engineers have to study

事实细节题。由于对电梯的抱怨增多，经理派工程人员调查具体情况。