And 30 an opinion is formed, most of their thinking then is simply trying to find support for it.
答案：(C) once
連接詞 once 表示「一旦……就……」，語意為「而一旦意見形成，他們隨後大部分的思考就只是在為這個意見尋找支持的證據」，呼應整段文章批評人類「先決定後思考」的心理現象；unless（除非）、even（甚至，不能這樣單獨作連接詞）都不合；though（雖然）會讓語意變成「雖然意見形成了，卻只是在找支持證據」，轉折邏輯反而不如once的時間先後因果關係自然。
once 在你腦中多半只有兩個意思：「一次」（once a week）與「曾經」（I once lived there）。這兩個都是副詞，突然要它當連接詞帶一整個子句，感覺很陌生，於是就放掉了。答對率 47%，這個字性上的落差是主因。
先看句構。空格後面是 an opinion is formed，是一個完整子句；逗號後面又是一個完整子句 most of their thinking then is simply trying to find support for it。兩個完整子句要接在一起，空格非放連接詞不可。even 是副詞，不能單獨連接子句，要當連接詞得寫成 even if 或 even though，字性上直接出局。先問「這個字能不能單獨當連接詞」，是這一題最快的刷法。剩下三個都是連接詞，就改比語意。once 當連接詞是「一旦…就…」，強調前後的時間先後與必然結果，而且副詞子句習慣用現在式代替未來式或表通則，句中的 an opinion is formed 正是現在式的被動。語意也完全吻合：意見一旦形成，後續的思考就只剩下替它找理由。though（雖然）表讓步，會變成「雖然意見形成了，他們的思考卻只是在找支持」——但這兩件事之間並不互相牴觸，讓步關係根本不成立。unless（除非）等於 if... not，會變成「除非意見形成，否則思考只是在找支持」，語意剛好顛倒。最後回頭對主旨：第一句 Most human beings actually decide before they think. 講的就是先有結論、再補理由。填 once，整篇的邏輯才收得起來。順帶注意句中的 then（那時、接下來）：它與 once 前後呼應，標示的正是「意見形成之後」那個時間點，也是 once 的旁證。
though（雖然）：讓步關係不成立，前後兩件事並不衝突。unless（除非）：等於 if not，代進去語意與全篇相反。even（甚至）：副詞，不能單獨連接兩個子句。
once（一旦…就…）、as soon as（一…就…）、even if（即使）、even though（儘管、雖然）、form an opinion（形成看法）、find support for（為…找到支持）。
Most human beings actually decide before they think. When people encounter a complex issue and form an opinion, how thoroughly have they 26 all the important factors involved before they make their decisions? The answer is: not very thoroughly, 27 they are executives, specialized experts, or ordinary people in the street. Very few people, no matter how intelligent or experienced, can 28 all the possibilities or outcomes of a policy or a course of action within just a short period of time.
Those who take pride in being decisive often try their best to consider all the factors beforehand. 29 , it is not unusual for them to come up with a decision before they have the time to do so. And 30 an opinion is formed, most of their thinking then is simply trying to find support for it.