This may not sound like much, but it could change the Earth's climate as 22 before.
答案：(B) never
as never before 意為「以前所未有的方式」：升溫幅度聽起來不大，卻可能以前所未有的程度改變地球氣候；ever、always、yet 都無法與 as…before 構成這個說法。
as ___ before 這個結構看起來像少了什麼，你可能想填 ever，因為 ever before 眼熟。但 ever 通常跟在比較級或否定詞之後（better than ever before、hardly ever），單獨接在 as 後面不成話。as never before 才是固定說法，意思是「以前所未有的方式、程度前所未見」：The country is changing as never before.（這個國家正以前所未有的方式改變。）
先看句子的語氣走向。本句用 This may not sound like much, but… 起頭（這聽起來似乎不多，但是…），這是一個先退後進的句式：前半先承認讀者的第一印象，後半要把它推翻。既然是推翻，後半必須把嚴重性拉高，而且拉得越高，這個轉折才站得住。四個選項裡只有 never 能把程度推到頂——「以前從來沒有過的程度」。前一句提到科學家預估未來一百年的升溫幅度是華氏二到六度，數字本身確實不起眼，正是這個句式要處理的第一印象。驗算法：把 as never before 換成中文的「前所未有地」唸一遍——它可能以前所未有的程度改變地球氣候，語氣與 but 的轉折對得上。看到 may not sound…, but… 這個形狀，就知道作者要推翻你的第一印象，答案一定落在「把程度拉高」那一側。
ever 如前所述不能單獨接在 as 之後，它需要比較級或否定詞來搭配。always 是「總是」，as always 確實是個說法，但意思是「一如往常」，放進來會變成「像往常一樣改變氣候」，語氣不但沒拉高，反而把事情說成常態，與 but 的轉折相反。yet 當副詞用於否定句與疑問句（not yet 尚未），也常見於 the best yet（目前為止最好的），但沒有 as yet before 這種說法，形式上就不成立。
as never before（以前所未有地）、better than ever before（比以往更好）、hardly ever（幾乎從不）、as always（一如往常）、not yet（尚未）、This may not sound like much, but…（這聽起來似乎不多，但…）。
Average global temperature has increased by almost 1°F over the past century. Scientists expect it to increase an 21 2° to 6°F over the next one hundred years. This may not sound like much, but it could change the Earth's climate as 22 before.
Climate change may affect people's health both directly and indirectly. For instance, heat stress and other heat-related health problems are caused directly by very warm temperatures. 23, human health can also be affected by ecological disturbances, changes in food and water supplies, as well as coastal flooding.
How people and nature 24 climate change will determine how seriously it affects human health. Generally, poor people and poor countries are 25 probable to have the money and resources they need to cope with health problems due to climate change.