Which one of the following water potential in soil is always positive

Answer: Option C

Gravitational potential is the water potential in the soil is always positive.
The gravitational potential is that portion of the total water potential that is due to the gravitational force field of the earth and is dependent on the vertical location of the water relative to the reference level.
The gravitational potential of soil water at each point is determined by the elevation of the point relative to some arbitrary reference level.