During such breaks, the mind turns inward, 19 it can subconsciously puzzle over subtle meanings and connections.
答案：(C) where
where 引導關係副詞子句，先行詞是前面的 the mind turns inward 所形成的「內在境地」；which 之後的子句已完整、無空缺，if 與 but 也無法與逗號前的敘述構成合理邏輯。
where 在你腦中大概只能指「地方」——公園、學校、城市；一看到前面沒有具體地點，就把 where 排除掉。事實上 where 引導的關係副詞子句，先行詞不必是實體場所，也可以是抽象的「情境、境地、狀態」。
關代與關副的分別，不是看先行詞，是看空格後面的子句完不完整。關係代名詞要在形容詞子句裡當主詞或受詞，所以後面接的是不完整子句；關係副詞是副詞，不佔主詞或受詞的位置，所以後面接的是完整子句。本句 it can subconsciously puzzle over subtle meanings and connections 主詞 it、動詞 puzzle over、受詞 subtle meanings 俱全，是完整子句，所以選關係副詞 where。where 是表地點或狀態的關係副詞，先行詞不限於實際的地方，也可以是表示情況的抽象名詞，例如 a situation where…（在…的情況下）、cases where…（在…的案例中）。本句的 the mind turns inward（心思轉向內在）指的就是一種心理狀態。課本學過的 This is the house where I was born. 也是同一個結構。
if 引導條件，但前後不是條件關係；but 表轉折，然而「心思轉向內在」與「琢磨細微意義」是順承而非對比。
a situation／case where…（在…的情況／案例中）、the reason why …（…的原因）、the time when …（…的時候）、puzzle over（苦思）、turn inward（轉向內在）。其中 the reason why … 這一組考過 5 個年度，83 年第 17 題 →、89 年第 25 題 →、92 年補考第 21 題 →、98 年第 23 題 →都出現過；the time when … 考過 3 個年度，83 年第 17 題 →、89 年第 25 題 →都出現過。
It has long been assumed that creativity is some unusual trait enjoyed by the few. However, according to a wide array of scientific and sociological research, creativity is 16 a sign of rare genius than a natural human potential. Thus, it can be nurtured and encouraged.
It is believed that taking breaks from a problem can help 17 a moment of insight or stimulate new ideas. Unconventional solutions can also be explored. That is why some of the most successful companies in the world, such as 3M and Google, encourage their employees to 18 all sorts of relaxing activities, such as playing pinball and wandering about the campus. During such breaks, the mind turns inward, 19 it can subconsciously puzzle over subtle meanings and connections.
Another way to increase creativity is to take risks. This is because many breakthroughs come up when people venture 20 their usual routines or areas of expertise. This can be done by, for example, learning new skills or traveling to new countries.