Let's match the diseases with their factors: - (A) Peptic ulcers are most commonly caused by infection with the bacterium Helicobacter pylori. So, A- (4) Bacteria. - (B) Dengue is a viral disease transmitted by mosquitoes. So, B-(1) Virus. - (C) Elephant Foot (Filariasis) is caused by parasitic worms (filarial worms) transmitted by mosquito bites. So, C-(3) Worm. - (D) Malaria is caused by Plasmodium parasites, which are protozoa, transmitted by mosquito bites. So, D-(2) Protozoa.