Concept:
Different infectious diseases are caused by different types of pathogens such as bacteria, viruses, and protozoa. Identifying the causative agent helps in proper diagnosis and treatment.
Step 1: Common cold.
Common cold is caused by viruses, mainly the Rhinovirus.
\[
\text{Common Cold} \rightarrow \text{Virus (B)}
\]
Step 2: Typhoid.
Typhoid fever is caused by the bacterium Salmonella typhi.
\[
\text{Typhoid} \rightarrow \text{Bacteria (A)}
\]
Step 3: Malaria.
Malaria is caused by the protozoan parasite Plasmodium and transmitted by the female Anopheles mosquito.
\[
\text{Malaria} \rightarrow \text{Protozoa (C)}
\]
Step 4: Write the correct matching.
\[
1-B, \quad 2-A, \quad 3-C
\]