18. A proposed ordinance requires the installation in new homes of sprinklers automatically triggered by the presence of a fire. However, a home builder argued that because more than ninety percent of residential fires are extinguished by a household member, residential sprinklers would only marginally decrease property damage caused by residential fires.

Which of the following, if true, would most seriously weaken the home builder’s argument?
A. most individuals have no formal training in how to extinguish fires.
B. Since new homes are only a tiny percentage of available housing in the city, the new ordinance would be extremely narrow in scope.
C. The installation of smoke detectors in new residences costs significantly less than the installation of sprinklers.
D. In the city where the ordinance was proposed, the average time required by the fire department to respond to a fire was less than the national average.
E. The largest proportion of property damage that results from residential fires is caused by fires that start when no household member is present.
我觉得选E, 答案是D. 为什么哪？