The correct answer is A) Amidships. When a vessel is loaded, the weight concentration amidships will cause the vessel's bottom to be subjected to tension stresses. This is because the weight of the cargo and the vessel itself creates a sagging effect on the hull, where the center portion dips down while the ends of the vessel rise up. This creates tension stresses on the bottom of the hull amidships. The other options are incorrect because weight concentration at the ends (B) or aft (C) or forward (D) would not cause tension stresses on the bottom of the hull amidships, but rather compression stresses or bending stresses in those specific areas.