How is a bacteriophage known?

Which of the following are proteinaceous infectious agents?

Lichen is usually cited as an example of 'symbiosis' in plants where an algal and a fungal species live together for their mutual benefit. Which of the following will happen if algal and fungal partners are separated from each other?
$A$. Both will survive and grow normally and independent from each other.
$B$. Both will die.
$C$. Algal component will survive while the fungal component will die.
$D$. Fungal component will survive while algal partner will die.
Based on your answer,how do you justify this association as symbiosis?

Which organisms are sensitive to $SO_2$ pollution?

Lichens indicate $SO_2$ pollution because they

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