The correct answer is A. ISMB.
The ISMB is the heaviest I-section for the same depth because it has the largest flange area. The flange area is the cross-sectional area of the flanges of an I-beam, and it is the main factor that determines the strength of an I-beam. The ISMB has a flange area of 12.5 square inches, while the ISLB has a flange area of 10.5 square inches, the ISHB has a flange area of 8.5 square inches, and the ISWB has a flange area of 6.5 square inches.
The ISLB, ISHB, and ISWB are all lighter than the ISMB because they have smaller flange areas. However, they are still strong enough to be used in a variety of applications. The ISLB is often used in light-duty construction, while the ISHB and ISWB are often used in heavy-duty construction.
The ISMB is the heaviest I-section for the same depth, but it is also the most expensive. The ISLB, ISHB, and ISWB are all less expensive than the ISMB, but they are also less strong. The choice of which I-section to use depends on the specific application.