S1 문장의 [______]에 들어갈 단어는?

난이도 필수 · 힌트를 덜 열수록 높은 점수 (현재 5점)
Perhaps not surprisingly, given how long [______] have been developing their craft, a lot of creativity in magic is of the tweaking variety - some of the most skilled and inventive magicians gained fame by refining the execution of tricks that have been known for decades, or sometimes centuries.