The correct answer is: A. Hypertonic environment.
Salts and sugars work to preserve foods by creating a hypertonic environment. This means that the concentration of salt or sugar in the food is higher than the concentration of salt or sugar in the surrounding environment. This causes water to move out of the cells of bacteria and other microorganisms, which kills them.
Option B, lower pH, is incorrect because it is not the main mechanism by which salts and sugars preserve foods. However, a lower pH can also help to kill microorganisms.
Option C, depletion of nutrients, is incorrect because salts and sugars do not typically deplete nutrients from foods. However, they can make some nutrients less available for absorption by the body.
Option D, lower osmotic pressure, is incorrect because it is not the main mechanism by which salts and sugars preserve foods. However, a lower osmotic pressure can also help to kill microorganisms.