Viruses are ...........

Match the following columns.

Column $I$	Column $II$
$(A)$ $DJ$ Ivanowsky	$(i)$ Viroids
$(B)$ $MW$ Beijerinck	$(ii)$ Crystallised virus
$(C)$ $WM$ Stanley	$(iii)$ Contagium vivum fluidum
$(D)$ $TO$ Diener	$(iv)$ Mosaic disease of tobacco

Viroids were discovered by $..........$.

Assertion $A$: Viruses are considered as a link between living and non-living organisms.
Reason $R$: Viruses are non-living,but they are obligate parasites in living cells.
Which option is correct for Assertion $A$ and Reason $R$?

The term $Contagium \text{ } vivum \text{ } fluidum$ for viruses was coined by:

The ultrastructure of bacteriophage $T$ was studied by: