In a healthy cell, the rate of DNA repair is equal to the rate of DNA mutation. When the rate of repair lags behind the rate of mutation, what is a possible fate of the cell?

The possible fate of the cell that it may turn cancerous.

Explanation:

The cells present in the body generally work in harmony. However, if a cell attains a mutation, it can make it proliferate in the case when it should not do, and make it thrive in the case when other cells are dying. Due to proliferation, the unusual cell produces more abnormal cells also known as cancerous cells. These cancerous cells become more favorable in comparison to the normal cells due to the phenomenon of natural selection. These cells eventually result in a lethal form of tumors.  

In the normal cells, the destructed gene or the damaged cells get repaired easily, in case if the damage is worse the cell dies. A protein known as p53 helps in repairing damaged cells or kills them if the damage is too severe. But in the case of cancer cells, the p53 protein does not work appropriately as they possess a mutated or changed form of p53 protein. Thus, in the case of cancerous cells, the rate of repair lags behind the rate of mutation, which makes the cancer cells thrive and increase in numbers resulting in further destruction.  

b.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.