Which of the following is a very good pollution indicator?

$A$: Viruses are considered as a link between living and non-living organisms.
$R$: Viruses behave as inert,non-living particles in a free state,while they exhibit active,living behavior inside a host cell.

Asexual reproduction in lichens occurs through which of the following? $(i)$ Pycniospores $(ii)$ Zoospores $(iii)$ Aplanospores $(iv)$ Soredia $(v)$ Apothecia

$A$ virus is considered a living organism and an obligate parasite when inside a host cell. However,viruses are not classified along with bacteria or fungi. What are the characteristics of a virus that are similar to non-living objects?

Mad cow disease is caused by $ . . . . . . $.

Which of the following are most suitable indicators of $SO_2$ pollution in the environment?