The correct answer is D. High pressure raises the boiling point of water.
When water is heated, it turns into steam. The boiling point of water is the temperature at which water turns into steam. The boiling point of water is 100 degrees Celsius at sea level. However, the boiling point of water can be increased by increasing the pressure. This is because the higher the pressure, the harder it is for water molecules to escape from the liquid state.
In a pressure cooker, the pressure is increased by trapping the steam inside the cooker. This increases the boiling point of water, which means that the water can be heated to a higher temperature without boiling. This higher temperature cooks the rice faster.
Option A is incorrect because the pressure cooker does not always let the steam escape. The steam is trapped inside the cooker, which increases the pressure.
Option B is incorrect because high pressure does not crush the hard covering of rice grains. The hard covering of rice grains is called the bran. The bran is removed when the rice is milled.
Option C is incorrect because the pressure cooker does not let the heat energy escape easily. The heat energy is trapped inside the cooker, which increases the pressure.