Where did the new cells come from?

Previously existing cells

All new cells come from previously existing cells. New cells are formed by karyokinesis - the process in cell division which involves replication of the cell's nucleus and cytokinesis-the process in cell division which involves division of the cytoplasm.

It comes from pre-existing cells

Step-by-step explanation:

Cells can only be formed when another cell divides to make 2 "daughter cells" that have the same DNA. Sometimes 2 cells will join to form one, such as a fertilized egg cell. Their DNA is combined in the new cell.