24 a circumstance often preconditions teenagers to the possibility of taking other drugs such as marijuana, cocaine or heroin.
答案：(D) Such
Such a circumstance（這樣的情況）指代前一句提到的情形，作句子主詞，符合承接前文、指代具體情境的語意。Since（自從/因為）、As（當/如同）都不能修飾名詞構成主詞、All 語意不合，皆不符合。
Since 與 As 都很眼熟，你會直覺把這一格讀成「因為……」或「當……時」，然後開始找後面的子句。
答對率四成二，鑑別度高達 54。先數句子成分：空格後面是 a circumstance（一個單數名詞組），再往後是 often preconditions（動詞），整句缺的是主詞。所以空格要填的必須是一個能修飾 a circumstance、把它變成主詞的字。Since 與 As 是連接詞，後面要接完整的子句，不能直接掛在一個名詞組前面；All 後面接複數或不可數名詞，不能接 a。只剩 Such——such a ＋ 單數名詞就是「這樣的一個……」。填進去讀成 Such a circumstance often preconditions teenagers...（這樣的情況往往讓青少年更容易……）。而「這樣的」指的就是前一句那個狀況：習慣性飲酒的人覺得酒精不夠刺激、想找更刺激的東西。
Since（因為、自從）與 As（當……時、因為）都是連接詞，形態上就接不起來；All 若要接 circumstance 得寫成 All circumstances（複數），這一句用的是 a circumstance。
such a ＋ 單數名詞（這樣的一個……）、such ＋ 複數名詞（這樣的……）、precondition somebody to（使某人預先傾向於）、habitual drinkers（習慣性飲酒的人）、stimulating（刺激的、令人振奮的）、seek other substances（尋求其他物質）。
Recent studies have shown that alcohol is the leading gateway drug for teenagers. Gateway drugs are substances people take that 21 them to take more drugs. Alcohol works directly on the central nervous system and alters one's moods and limits judgment.
Since its way of altering moods (changing one's state of mind) is generally expected and socially acceptable, oftentimes it 22 over drinking. Habitual drinkers may find alcohol not stimulating enough 23 and want to seek other more stimulating substances. 24 a circumstance often preconditions teenagers to the possibility of taking other drugs such as marijuana, cocaine or heroin.
Another reason why alcohol is the main gateway drug is that the 25 of teenagers it can affect is very wide. It is easily accessible in most societies and common in popular events such as sports gatherings and dinner parties.