To what does "descent with modification" refer? a. All species come from preexisting species and are changed over time.
b. All species come from preexisting species but stay basically the same.
c. Some species come from preexisting species and are changed over time.
d. Some species come from preexisting species but stay basically the same.

Pls me i need this ! each cell has genes activated depending on it's job and what kind of cell it is. it is the presence of that causes the repressor protein to fall off and unblock the gene on the lac operon. if a gene is turned on then it is being an additional circular chromosome found in some bacteria that is used in genetic engineering.