What does the part labeled $''A''$ in the given figure represent?

Viruses can pass through which of the following?

Choose the correct option for the following statements:
$(i)$ The name virus,meaning venom or poisonous fluid,was given by $Pasteur / D. J. Ivanowsky$.
$(ii)$ $W. M. Stanley / T. O. Diener$ discovered viroids.

Which organisms cannot grow in polluted areas?

Which of the following is $NOT$ true for lichens?

Lichens are useful as: