To answer this question, the user needs to know about the different types of substances and their properties.

The correct answer is C. Solid carbon dioxide.

Explanation for each option:

A. Liquid nitrogen: This option is incorrect. Liquid nitrogen is a colorless, odorless, and tasteless liquid that is commonly used as a refrigerant. It is not dry ice.

B. Water ice: This option is incorrect. Water ice is a frozen form of water. Although it is a solid, it is not dry ice.

C. Solid carbon dioxide: This option is correct. Dry ice is the solid form of carbon dioxide, which is a gas at room temperature. It gets its name because it does not melt into a liquid, but rather sublimates directly into a gas.

D. Frozen ethanol: This option is incorrect. Ethanol is a clear, colorless liquid that freezes at a temperature of -114 degrees Celsius. Although it is a solid at very low temperatures, it is not dry ice.

Therefore, the correct answer is C. Solid carbon dioxide.