Which description best characterizes a Riemann sum that uses the function value at the point halfway between the endpoints of every equal-width subinterval on [a,b]?
a) The height of each rectangle equals f evaluated at the left endpoint of the subinterval.
b) The height of each rectangle equals f evaluated at the point halfway through the entire interval [a,b].
c) The height of each rectangle equals f evaluated at the point halfway between the subinterval’s endpoints.
d) The height of each rectangle equals the average of the function values at the two endpoints of the subinterval.