Which of these diseases cannot be controlled by killing the vectors?

Explanation

Some diseases are transmitted through vectors such as mosquitoes and flies. Controlling these vectors can help reduce the spread of the disease. However, not all diseases can be controlled by killing the vectors. The question is asking which of the diseases listed cannot be controlled by killing the vectors. Option A is River blindness, which is transmitted by the blackfly. Killing the blackfly can help control the spread of the disease. Option B is Malaria, which is transmitted by the female Anopheles mosquito. Killing the mosquito can help control the spread of the disease. Option C is Polio, which is not transmitted by a vector but rather through contaminated food and water or contact with an infected person. Controlling vectors would not have any effect on the spread of the disease. Option D is Cholera, which is also not transmitted by a vector but rather through contaminated food and water. Controlling vectors would not have any effect on the spread of the disease. Therefore, the correct answer is Option D. In summary, not all diseases can be controlled by killing the vectors. Diseases such as Polio and Cholera are not transmitted by vectors and therefore controlling vectors would not help control the spread of the disease.