Final answer:
Option (A), L'Hôpital's Rule is the method used to determine infinite limits, it involves differentiating the numerator and denominator until the limit can be evaluated.
Step-by-step explanation:
The method commonly used to determine infinite limits is a) L'Hôpital's Rule. L'Hôpital's Rule helps to calculate the limit of indeterminate forms by differentiating the numerator and denominator separately until a determinate form is obtained which can then be evaluated for the limit. It is important to note that the other options, such as Riemann Sums, Mean Value Theorem, and Chain Rule, have different applications within calculus.