费费逻辑79

Questions 78-79
Despite improvements in treatment for asthma, the death rate from this disease has doubled during the past decade from its previous rate. Two possible explanations for this increase have been offered. First, the recording of deaths due to asthma has become more widespread and accurate in the past decade than it had been previously. Second, there has been an increase in urban pollution. However, since the rate of deaths due to asthma has increased dramatically even in cities with long-standing, comprehensive medical records and with little or no urban pollution, one must instead conclude that the cause of increased deaths is the use of bronchial inhalers by asthma sufferers to relieve their symptoms.
79. Which one of the following is an assumption on which the argument depends?

A.Urban pollution has not doubled in the past decade.
B.Doctors and patients generally ignore the role of allergies in asthma.
C.Bronchial inhalers are unsafe, even when used according to the recommended instructions.
D.The use of bronchial inhalers aggravates other diseases that frequently occur among asthma sufferers and that often lead to fatal outcomes even when the asthma itself does not.
E.Increased urban pollution, improved recording of asthma deaths, and the used of asthma deaths, and the use of bronchial inhalers are the only possible explanations of the increased death rate due to asthma.

这道题A为什么错呢，这个不是排除他因吗？取非，如果城镇人口增加了2倍，那么死亡人数的增加就有可能不是由于使用bronchial inhalers 造成的，这样不是就使原文的结论不成立了吗？