To solve this problem, we need to match the diseases with their causative organisms. Let's analyze each disease:$\newline \bullet$a. Typhoid:$\newline$ - Typhoid is caused by the bacterium Salmonella.$\newline$ - This matches with iii.$\newline \bullet$b. Pneumonia:$\newline$ - Pneumonia can be caused by several organisms, but Haemophilus influenzae is a common bacterial cause.$\newline$ - This matches with iv.$\newline \bullet$c. Filariasis:$\newline$ - Filariasis is caused by parasitic worms, with Wuchereria bancrofti being a primary causative agent.$\newline$ - This matches with i.$\newline \bullet$d. Malaria:$\newline$ - Malaria is caused by the Plasmodium parasite.$\newline$ - This matches with ii.$\newline$Now, let's match the diseases with their causative organisms:$\newline a \rightarrow iii, b \rightarrow iv, c \rightarrow i, d \rightarrow ii \newline$This corresponds to Option 1.