The expression ((1/20)(√1/20 + √2/20 + √3/20 + ____₊ √20/20)) is a Riemann sum approximation for:
a) ∫₀¹√(x) dx
b) ∫₀¹√(1 - x) dx
c) ∫₀¹x² dx
d) ∫₀¹eˣ dx