Whenever a sheet is stamped or stretched, different spots on it end up with different combinations of major and minor surface strain, and some of those combinations are safe while others are right on the edge of tearing. A forming limit diagram plots exactly this, major strain against minor strain, with a curve marking where necking or fracture starts, so measuring strains on an actual stamped part and plotting them against that curve tells an engineer whether the part was formed safely. This whole idea is specific to stretching and drawing sheet metal and has nothing to do with pouring castings, welding joints, or heat treating. So an FLD is used for sheet metal formability analysis, option (B).