Which is a part of the cell theory?

a) cells come from pre-existing cells

b) cells have a nucleus

c) organisms with one cell must be seen with a microscope

d) organisms must have more than one cell to live

The first statement is a part of the cell theory, cells come from pre-existing cells. Not all cells have a nucleus, all the prokaryotes lack nuclei.

There are one-celled organisms and some types of cells can be so small that they need super magnifying microscopes in order to be observed (more powerful than the regular light microscopes)