The correct option is D Vacillation
Vacillation is the inability to decide between different opinions or actions; indecision. For example, "the First Minister's vacillation over the affair". Hence, Option D is correct. Among the rest of the options, adaptability means the quality of being able to adjust to new conditions, instability means the state of being unstable, versatility means ability to adapt or be adapted to many different functions or activities. These options do not express the intended meaning, hence incorrect.