Final answer:
The amount of energy added to the gravitational field is 90 J.
Step-by-step explanation:
The amount of energy added to the gravitational field can be determined by calculating the gravitational potential energy. Gravitational potential energy is given by the equation U = mgh, where U is the potential energy, m is the mass, g is the acceleration due to gravity, and h is the height. In this case, if you did 90 J of work to elevate a bucket of water, the energy added to the gravitational field is also 90 J.
Therefore, the correct answer is A. 90 J.