Which of the following acts as a pollution indicator?

Assertion $A$: Viroids and viruses can pass through bacteria-proof filters.
Reason $R$: Bacteria are retained by bacteria-proof filters.
Which option is correct for Assertion $A$ and Reason $R$?

Which of the following is correct about viroids?

What does a virus contain?

The viruses responsible for causing polio and hydrophobia are

The concept of "Contagium vivum fluidum" was given by