You isolate cells from a tumor and study them. You observe that the cells continue dividing, even when DNA is damaged, when the cells become crowded, or even when nutrients run low. These observations lead you to suspect that the cells

Cells are cancerous

Explanation:

Cancer is a disease which is caused by the continuous division of the cells without differentiation. The differentiation is the important process which determines the fate of the cell in the body that is it provides the function to the cell it has to perform.

In the given question, when the cells are dividing continuously and form a tumour even in the low condition therefore it can be concluded that the cells are cancerous or will be the cause of cancer.

Thus, Cells are cancerous is correct.