To solve this problem, we need to match each disease with its correct type of vaccine. Let's analyze each disease:$\newline \bullet$a. Tuberculosis:$\newline$ - The vaccine for tuberculosis is the BCG vaccine, which uses a harmless strain of bacteria.$\newline$ - This matches with iv. Harmless bacteria.$\newline \bullet$b. Whooping cough:$\newline$ - The vaccine for whooping cough is the DTP vaccine, which includes a component for whooping cough made from killed bacteria.$\newline$ - This matches with iii. Killed bacteria.$\newline \bullet$c. Diphtheria:$\newline$ - The vaccine for diphtheria is a toxoid vaccine, which uses an inactivated toxin.$\newline$ - This matches with ii. Inactivated toxin.$\newline \bullet$d. Polio:$\newline$ - The vaccine for polio can be an oral polio vaccine (OPV), which uses a harmless virus.$\newline$ - This matches with i. Harmless virus.$\newline$Now, let's match the diseases with their corresponding vaccine types:$\newline a \rightarrow iv, b \rightarrow iii, c \rightarrow ii, d \rightarrow i \newline$This corresponds to Option 3.