
Passage: Leishmaniasis is an infectious disease. The disease is spread by sand flies biting sick mice and then biting people. When building a new town in an area, although leishmaniasis and sand flies are swords in that area, epidemic experts warn that stepping up efforts to eliminate rats to reduce the number of rats will do more harm than good.
Question: If the above statement is true, which of the followings best confirms the warning of the expert?
A. A.Rats infected with leishmaniasis have little chance of passing the disease directly to humans.
B. B.Leishmaniasis is more contagious in rats than in humans.
C. C.Sand flies that do not transmit leishmaniasis do little harm to human health.
D. D.Sand flies bite people only when there are not enough rats.
Answer: