Fill in the Blanks (Reading & Writing)

Clockmaking was once a highly specialised craft, with apprentices spending years learning to —assembleassemblesassemblingassembled tiny gears and springs by hand. A skilled clockmaker had to understand not only mechanics but also the —subtlesubtlysubtletysubtleness effects of temperature on metal, since expansion could throw a mechanism out of time. Although quartz movements later made hand-built clocks less common, traditional clockmaking still —thrivesthrivethrivingthrived among collectors today.