You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: SCIENCE "T"ALK 
Clue: It's what the "t" stands for in tRNA
transfer

Category: DESIGN 
Clue: Derived from scutum, the Latin for "shield", it's a shield bearing a coat of arms, or a metal plate around a keyhole
escutcheon

Category: U.S. COINS 
Clue: The Coinage Act of 1965 removed all of this metal from dimes & quarters

silver