S1 문장의 [______]에 들어갈 단어는?

난이도 고난도 · 힌트를 덜 열수록 높은 점수 (현재 5점)
For every toxic substance, process, or product in use today, there is a safer alternative ― either already in existence, or waiting to be discovered through the application of human intellect, [______], and effort.