The correct option is D (a) and (b) above.
∙ Mosquitoes lay their eggs in open stagnant water. So, we should keep our surroundings clean.
∙ Mosquitoes feed on blood. So, we should properly cover ourselves with clothes.
∙ Insecticides can be used to kill mosquitoes. It should be sprayed in areas where a large number of mosquitoes are present.