The correct answer is: A. Is dry.
Retaining walls are designed to support a mass of earth, and the stability of the wall depends on the properties of the earth. One of the most important properties is the moisture content of the earth. If the earth is too wet, it will be more likely to move and cause the wall to fail. Therefore, retaining walls are typically designed to assume that the retained earth is dry.
Option B is incorrect because it is not possible for the retained earth to be free from moisture. Even if the earth is initially dry, it will eventually absorb moisture from the air or from groundwater.
Option C is incorrect because cohesive earth is earth that has a strong tendency to stick together. This type of earth is more stable than non-cohesive earth, and retaining walls are not typically designed to assume that the retained earth is non-cohesive.
Option D is incorrect because it is not possible for the retained earth to meet all of the conditions listed. The correct answer is A. Is dry.