When the degree of saturation is zero, the soil mass under consideration represents A. one phase system B. two phase system with soil and air C. two phase system with soil and water D. three phase system

The correct answer is A. one phase system.

When the degree of saturation is zero, the soil mass is completely dry. This means that there is no water present in the soil, and the soil mass is made up of only one phase: solid particles.

Option B is incorrect because a two phase system would have two distinct phases: solid particles and water. Option C is incorrect because a two phase system would have two distinct phases: solid particles and water. Option D is incorrect because a three phase system would have three distinct phases: solid particles, water, and air.