The maximum spacing of vertical stiffeners is (where d is the distance between flange angles) A. 1.33 d B. 1.25 d C. 1.5 d D. 1.75 d

The correct answer is A. 1.33 d.

The maximum spacing of vertical stiffeners is 1.33 times the distance between flange angles. This is to ensure that the stiffeners are able to provide adequate support to the web of the beam and prevent it from buckling.

The other options are incorrect because they do not provide adequate support to the web of the beam.