31.   When they infect the skin cells, the cells begin pumping out the proteins, and the body mounts an immune response.

32.   When they fall to a certain length, the cell begins to age and eventually stops dividing.

33.   When treated with specific proteins, the cells began to grow different types of tissue cells.

34.   Breast cancer occurs when cells that normally line the ducts through which a woman lactates begin a process of uncontrolled multiplication.