Derivative at a Point & Derivative Functions - Lecture 8 (Calculus 1)

Geometrically, what does the derivative f'(a) measure on the graph of f?

1. A.The y-coordinate of the point (a, f(a)) on the graph
2. B.The slope of the tangent line at the point (a, f(a))
3. C.The signed area under f from x = 0 up to x = a
4. D.The vertical distance from the point (a, f(a)) to the x-axis