The best answer is join. The relationship between the first pair of words, instant and gradual, is that of antonyms—words that have opposite meanings. Therefore, the second pair of words must also be antonyms. Join is an antonym of quit.
Yesterday's Analogy Quiz
Tomorrow's Analogy Quiz
About Infoplease, Part of Family Education Network
© 2000–2016 Sandbox Networks, Inc., publishing as Infoplease