The state of the soil when plants fail to extract sufficient water for their requirements, is

ANS:B - permanent wilting point

Answer is option D (none of these).

Permanent wilting point is defined as that moisture content below which plants can no longer extract sufficient water from soil for their growth requirements.

So.

The water at which soil fail to extract sufficient water for their requirement is below permanent welting point that is ultimate welting point.

So, the Ultimate welting point is the correct answer whis is not given in options.