Tea and coffee contain caffeine, a substance that can make you active. 26 you do not feel fully engaged after you wake up in the morning, drinking coffee at breakfast can mean the 27 between a productive day and never arriving at work.
答案：(C) If
If在這裡引導條件子句，「如果你早上起床後感覺還沒完全清醒」，符合條件句邏輯；Although（雖然）、Because（因為）、Unless（除非）都不合。
本題大考中心未公布逐題答對率，以下不談數據，只談觀念。
四個選項都是從屬連接詞，而「早上起床沒精神所以喝咖啡」聽起來很像因果，Because 很誘人。這一格要看主要子句裡那個 can。
四個選項都是從屬連接詞，可見這一格考的是前後兩件事的關係。先讀整句：___ you do not feel fully engaged after you wake up in the morning, drinking coffee at breakfast can mean the difference between a productive day and never arriving at work.（……你早上醒來後覺得還沒完全進入狀況，早餐喝杯咖啡就可能是「有生產力的一天」與「根本到不了公司」之間的差別。）關鍵在主要子句用的是 can mean（可能意味著）——講的是一種可能的結果，不是既成的事實。再看這一整段的口吻：它是在對讀者說明咖啡因的作用，讀者不一定每天早上都沒精神；所以這是一個假設的情境「如果你……那麼……」，填 If。
Because（因為）：它預設「你早上就是沒精神」是既定的事實，但作者面對的是所有讀者，不能替每個人斷定；而且既定事實配上 can（可能）語氣也不搭。Although（雖然）：讓步要求前後牴觸，但「沒精神」與「喝咖啡有差別」是順著走的。Unless（除非）：意思會變成「除非你沒精神，否則喝咖啡才有差別」，把邏輯整個顛倒了。
If ＋ 子句（如果）、feel engaged（進入狀況、投入）、a productive day（有生產力的一天）、contain caffeine（含咖啡因）、a substance（物質）、make sb active（使某人有活力）。
Tea and coffee contain caffeine, a substance that can make you active. 26 you do not feel fully engaged after you wake up in the morning, drinking coffee at breakfast can mean the 27 between a productive day and never arriving at work.
Caffeine is also the main ingredient in many "diet pills." It boosts metabolism, thereby 28 the body to burn more calories. If you take a 29 to a different time zone, caffeine can help you overcome jet lag. Most hotels have coffee and tea service in the room for this very reason.
Every individual handles caffeine differently. For some people, a single cup of coffee in the morning will make them feel nervous and 30 them up all night. Other people can down five cups and be perfectly calm.