ANS:A - Rivets

Among the options provided, rivets are considered a permanent fastening method. Rivets are mechanical fasteners consisting of a cylindrical shaft with a head on one end. They are inserted into aligned holes in two or more pieces of material and then deformed or "set" to permanently join the materials together. This deformation creates a second head, or "shop head," on the opposite end of the shaft, effectively clamping the materials in place. Once rivets are installed, they cannot be easily removed without damaging the materials they join. This permanence makes rivets a preferred choice for applications where a secure and long-lasting connection is required, such as in construction, aerospace, automotive, and structural engineering. While bolts and screws can also provide strong and secure connections, they are generally considered removable fasteners because they can be unscrewed or unthreaded from the materials they fasten. Keys are typically used for temporary or semi-permanent fastening and are not generally considered permanent fasteners.