Pox viruses contain which of the following vitamins?

Who demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants?

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 $R$?

The causative agent of mad-cow disease is a

Which organism is formed by the symbiotic association between algae and fungi?

$A$ bacteriophage is