Epidemiology deals with the study of

$A$ child would develop mental illness if one does not get:

Steroids are used in:

The polio vaccine was developed by:

Which of the following statements are correct?
$(1)$ Yoga is practiced to achieve physical and mental health.
$(2)$ Infectious diseases are very common; all of us have suffered from one or the other at some time.
$(3)$ $AIDS$ is an infectious disease.
$(4)$ Cancer is a non-infectious disease.
$(5)$ $A$ healthy person contributes to economic prosperity.

$A$ disease like dengue is spread by: