II. A post tapers uniformly from a diameter d at the upper end to a larger diameter D at the lower end, as shown. It supports an axial load of P. Given allowable stress of S, the post's dimension can...

Extracted text: II. A post tapers uniformly from a diameter d at the upper end to a larger diameter D at the lower end, as shown. It supports an axial load of P. Given allowable stress of S, the post's dimension can be determined using the formula o=P/A. For structural safety, what must be the area in this formula? The lower, middle, or upper cross- section of the post? Why? Upper Area Middle Area Lower Area