With all Logical Reasoning style GRE Reading Comprehension questions, first identify the question task which in this case is to find something that weakens "the view that surgical mortality rates could be reduced by raising operating room temperatures".

Now, evaluate the choices seeking one that provides new information that would potentially weaken the plan to raise the temperature in operating rooms, while eliminating choices that are vague, require additional information, strengthen the plan, or have no impact on the plan.

A. Surgical mortality rates are slightly higher during summer months than during winter months.
Requires additional information, because it is not known whether temperatures outside affect the operating room temperatures. Eliminate.

B. Delivery rooms tend to be kept at slightly higher temperatures than other operating rooms (around 24°C or 75.2°F) because premature babies are especially vulnerable to hypothermia.
No impact, because what happens in delivery rooms has no clear and direct impact on the mortality rate in operating rooms. Eliminate.

C. It is more costly to maintain surgical equipment at temperatures above 21°C.
No impact, because cost of maintenance has no clear and direct impact on the mortality rate in operating rooms. Eliminate.

D. Nurses and medical technicians prefer working in room temperatures less than 24°C.
No impact, because what nurses and medical technicians prefer has no clear and direct impact on the mortality rate in operating rooms. Eliminate.

E. Manual dexterity and mental alertness tend to decline as the temperature rises above 21°C and more significantly so at temperatures above 24°C.
Weakens the argument, because if dexterity and mental alertness decline as the temperature rises this would have a clear negative impact on the mortality rate in operating rooms. Select.

Select Choice E.