Habitual drinkers may find alcohol not stimulating enough 23 and want to seek other more stimulating substances.
答案：(B) after a while
after a while 意為「過一段時間之後」：習慣性飲酒者過一陣子會覺得酒精刺激不夠，轉而尋求更強的物質；in advance（事先）、in the least（一點也不）、at most（至多）語意都不合。
答對率 37%。
while 你最熟的是連接詞「當…時」，不太容易想到 a while 是名詞片語「一段時間」：after a while（過一陣子）、for a while（有一陣子）、in a while（再過一會兒）、once in a while（偶爾）。「while 當名詞時一定要加 a」，這是與連接詞用法最好分辨的地方。
主詞是 Habitual drinkers（習慣性飲酒者）——「習慣性」本身就隱含時間累積，喝久了才會覺得不夠刺激。前一句提到飲酒改變情緒的方式一般可預期、社會也能接受，本句接著講長期下來的變化，下一句再說這種情況會讓青少年更容易接觸其他毒品。整段是一條時間推移的線。
in advance 是「事先」，時間方向相反；in the least 用於否定句（not in the least 一點也不）；at most 是「至多」，用於數量。
after a while（過一陣子）、for a while（有一陣子）、once in a while（偶爾）、in advance（事先）、not in the least（一點也不）。
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.