Answer

a) Oil forms a barrier and prevents air from entering the water. The larvae hence lack the air to stay alive.

b) i) A shirt that has the smell produced by children infected with malaria is more attractive to mosquito A than a shirt that does not have that smell.

ii) A white shirt contrasts with the black mosquitoes more clearly, thus making the mosquitoes more visible. So, people can count the mosquitoes accurately. A black shirt, on the other hand, makes mosquitoes harder to spot.

iii) Mosquito A are attracted to the smell produced by infected people. This smell could be released in an unoccupied part of a house to lure the mosquitoes away from where people actually are. Alternatively, the container which stores the smell produced by infected people can be used to attract and trap mosquitos, which will then lead to fewer bites on people.