The correct answer is A. 100% regulation.
Regulation is a measure of how well a DC generator maintains a constant output voltage despite changes in load. A 100% regulation means that the output voltage remains constant even when the load changes by 100%. This is the ideal case, and it is not always possible to achieve 100% regulation in practice. However, the higher the regulation, the better the DC generator will be able to maintain a constant output voltage.
B. Infinite regulation is not possible, as there will always be some small variation in the output voltage due to factors such as changes in temperature and resistance.
C. 50% regulation is not as good as 100% regulation, as the output voltage will vary by 50% when the load changes by 100%.
D. 1% regulation is even worse than 50% regulation, as the output voltage will vary by 1% when the load changes by 100%.
In conclusion, 100% regulation is the preferred value for a DC generator.