Locations on a graph of a function that involve any discontinuity (removeable disc., jump disc., abrupt stop, or infinite disc.), a cusp, or a vertical tangent are considered to be "non-differentiable" because ... O you can not find the slope of the secant that crosses over such locations (that is, you can not find the slope of the line that connects a function point on the left of the location to a function point on the right of that location). O the secant that crosses over all such locations is always horizontal (that is, the line that connects a function point on the left of the location to a function point on the right of that location is always horizontal). O the tangent is always horizontal at all such locations. O you can not find the slope of the tangent at such locations