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% replaces any number of letters (la% - lake, lamp)_ replaces one letter (ca_ - car, cat)

Crossword clues for They travel at the speed of sound:

ECHOES: They travel at the speed of sound
SABRE: It travels with the speed of sound.
WHIP: Human-powered device part of which can travel faster than the speed of sound
CHUCKYEAGER: First pilot to travel faster than the speed of sound