Final answer:
The subject of this question is Mathematics and it is related to Riemann Sums.
Step-by-step explanation:
The given question is related to the topic of Riemann Sums. Riemann Sums are used to approximate the area under a curve by dividing it into smaller rectangles and calculating the sum of their areas. One way to choose the sample points for the Riemann sum is by using the left-endpoints of the rectangles. This means that the height of each rectangle is determined by the leftmost point on its base.
Therefore, the correct option for this question is A) Riemann Sums.