Learn from Mistakes

Thomas Edison tried two (27)________ different materials in search of a filament for the light bulb. When none worked satisfactorily, his assistant complained, that all their work was in vain, and they had learned (28)________. Edison replied very confidently, “Oh, we have come a long way and we have learned (29)________. We know that (30)________ so many elements which we cannot use to make a good light bulb.”