In what type of environment do hypertonic solutions cause cells to shrink?

Hypertonic solutions cause cells to shrink when they are placed in an environment where the concentration of solutes outside the cell is higher than the concentration inside the cell. In such scenarios, water moves out of the cell through the process of osmosis to balance the solute concentrations on both sides of the cell membrane. As water exits the cell, it leads to a decrease in cell volume, resulting in the cell appearing shriveled or smaller.

In contrast, when the concentration of solutes is equal, there is no net movement of water, and the cell retains its normal shape. If the concentration of solutes inside the cell is higher, water would flow into the cell, potentially causing it to swell or burst. A vacuum does not pertain to solute concentration and would not create a hypertonic environment; rather, it would likely lead to other physical phenomena unrelated to osmosis. Hence, option C correctly identifies the condition necessary for hypertonic solutions to cause cells to shrink.