As you observe an unknown cell under a microscope, you make the following observations.

There is one large, irregular structure that occupies about half the cell.

The cell has several small, green, circular objects inside it.

It has a medium-sized circular structure that appears to be a nucleus.

There is a thick, rigid structure that surrounds the cell.

What type of cell are you observing?

A: an animal cell

B: a bacterium

C: a protist

D: a plant cell