Here we have to take care that questioner is asking about which statement 'supports' our paragraph.It's not like 'which statement can be concluded from paragraph.
None of the options can be concluded from the paragraph.Option A,B,C are invalid while option D also can't be concluded as both Malaria and Dengue are caused by different kinds of mosquitoes so we can't say like if some region is affected by malaria then it would be affected by dengue.
But does our option D support our paragraph? Yes! because when there is malaria in some region then certainly there would be sufficient quantity of mosquitoes and that's Municipal authorities also concluded.