Question

begin as a single cell! that first cell grows and divides to form more cells.
a human begins as a single fertilized egg cell known as a zygote.
a teenage human is made of trillions of cells.
as the human body grows and develops, cells become specialized to do different jobs. these different types of cells are the building blocks of the organ systems that keep us alive.
complete the paragraph.
humans start out as many cells. as humans develop, they cells. cells specialize to perform jobs in the body.

Explanation:

The text states that humans begin as a single cell (zygote) which then divides to form more cells. So the first blank should be "a single cell" instead of "many cells". As the cell divides, the number of cells increases, so the second blank is "get more". And cells specialize to do "different" jobs as mentioned in the text.

Answer:

Humans start out as a single cell. As humans develop, they get more cells. Cells specialize to perform different jobs in the body.