Each group contains 6 words. 3 of these are related to each other. Indicate which 3 are thus MOST CLOSELY RELATED.
silver, platinum, amethyst, coinage, emerald, sapphire
orange, pear, lemon, grapefruit, prune, chocolate
79, 35, 47, 53, 42, 63
triangle, polygon, rhombus, trapezoid, square, geometry