To determine what happens to red blood cells when sugar is added to the solution, it is important to consider how osmosis works. When sugar is added to a solution, it increases the solute concentration of the solution, creating a hypertonic environment.
In a hypertonic solution, water moves out of the cells (which are in a lower concentration of solute) to balance the solute concentration on both sides of the cell membrane. This means that water leaves the red blood cells, causing them to shrink.
Therefore, the correct answer is: A. The red blood cells released water through osmosis to reach equilibrium with the surrounding solution.