The correct answer is: C. The field of that generator is weakened.
When the field of a generator is weakened, the generator will start to act as a motor. This is because the weakening of the field reduces the amount of current that is generated, which in turn reduces the amount of torque that is produced. This can cause the generator to start to rotate in the opposite direction, which is how a motor works.
The other options are incorrect because they would not cause the generator to act as a motor. Option A is incorrect because reversing the direction of the generator would not change the amount of current that is generated. Option B is incorrect because increasing the speed of the generator would increase the amount of current that is generated, which would make the generator act as a generator, not a motor. Option D is incorrect because taking a large share of loads would not change the amount of current that is generated.
In conclusion, the correct answer is: C. The field of that generator is weakened.