Quote:
In an attempt to discover the cause of malaria, a deadly infectious disease common in tropical areas, early European settlers in Hong Kong attributed the malady to poisonous gases supposed to be emanating from low-lying swampland. Malaria, in fact, translates from the Italian as “bad air.” In the 1880s, however, doctors determined that Anopheles mosquitoes were responsible for transmitting the disease to humans. The female of the species can carry a parasitic protozoan that is passed on to unsuspecting humans when a mosquito feasts on a person’s blood.
(A) The first follows from a mistaken conclusion about a topic in question; the second explicates the correct explanation of that topic.
Erroneously the thought the gasses were responsible for malaria BUT actually, the real reason to explain the disease is an insect
(D) The first identifies the cause of an erroneous conclusion; the second develops a premise to support the correct conclusion.
The first part of D more or less says the same thing the first part of A says. However, the second part does not develop a premise BUT is actually a real explanation for the cause. it is a conclusion per se. One step identified not a two steps process.
Hope this helps to catch the real essence of the question above.
Regards