In living things, cells must be in a solution where water leaves and enters the cell at .

isotonic; the same rate

Explanation:

Cell Theory as as commonly known gives the best definition for cells. All organisms that ever existed are made up of one or more cells. The theory state that the cell is a basic unit, that is of all living things, and that all cells come from cells that have existed.

For cell that is in an isotonic solution,no net flow of water into or out of the cell will be experienced, the volume of the cell is at a state of stability. When the level or concentration of solute in and out of the cell is at the same pace or level, the the cell membrane does not allow solutes to cross, leading to the solution being isotonic to the cell.

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answer: the correct option is d. enzyme

lactase and carbonic anhydrase are the examples of enzymes.

lactase is an enzyme, which is present in the small intestine of mammals. it in the digestion of the disaccharide, lactose ( milk sugar) by converting it into two monosachharide, which are glucose and galactose.

carbonic anhydrase is present in the red blood cells. this enzyme plays significant role in the transport of co₂. it in the conversion of co₂ and h₂o into carbonic acid, which is then dissociated into bicarbonate ions and hydrogen ions.