ILL MARK BRAINLIST FRIST ANSWER
Fry remembered a curious adhesive – a strong and yet easily removed “unglue”– that Spencer Silver . . . had come upon several years earlier. . . . Silver felt the unusual adhesive might have some commercial value. . . . At the time, no one had come up with a use for it, and so the formula for the weak adhesive was filed away – until the Monday morning when Fry came to work with the idea of making sticky bookmarks that could also be removed.

—The Evolution of Useful Things,
Henry Petroski

When did Spencer Silver discover the formula for the “unglue”?

A. several years before Fry had his idea
B. the year before Fry had his idea
C. at the same time Fry had his idea
D. soon after Fry had his idea