Which of the following are the chief 'producers' in the oceans?

Which kingdom consists of organisms that are simple,predominantly aquatic,and unicellular eukaryotes?

The accumulation of dead remains of diatoms at the bottom of the ocean is known as ...........

Diatomaceous earth is used to insulate boilers and steam pipes because:

Select the correct option for the following statements:
$(i)$ All protozoans are heterotrophs and live as predators or parasites.
$(ii)$ $Trypanosoma$ causes sleeping sickness.

The protists used in the construction of soundproof rooms are . . . . . . .