That is 20 green tea is so good for health.
答案：(D) why
【句型】That is why... 固定句型「這就是為什麼……」，承接前文原因，帶出結果；whether（是否）、whenever（每當）、what（這裡是解釋「為什麼」不是「什麼」）都不合。
That is ______ 這個開頭，很多人第一個想到的是 what，因為 what 在腦中就等於「什麼」，而 That is what... 也確實是常見句型。這一格要分辨的是：空格後面接的到底是「原因」還是「東西」。
把空格後面那一串單獨拿出來看缺不缺成分：green tea is so good for health 的主詞、動詞、補語全都齊了，一個名詞位置都不缺。what 進到子句裡一定要當主詞或受詞（它本身就等於 the thing that），這裡沒有空位給它，第一步就能刷掉。再看前後的邏輯：前面兩句講的是綠茶只乾燥不發酵、因此保留了有益的化學成分，這是「原因」；空格這一句 green tea is so good for health 是「結果」。前因後果，用 That is why（這就是為什麼）。順便把最常搞混的一組並排記起來：That is why ＋ 結果；That is because ＋ 原因。同一份考卷的第 27 題也在考 wh- 詞，那一題分的是「地方 vs 事物」，本題分的是「原因 vs 事物」，兩題可以對著看。
whether（是否）：引導的是「是不是」的問題，前文沒有任何待決定的疑問，That is whether... 在這裡講不通。whenever（每當）：引導時間子句，但前文給的是原因，不是時間點。what：理由如上，後面的子句不缺名詞位置，what 無處可放。
That is why（這就是為什麼，後接結果）、That is because（那是因為，後接原因）、be good for health（對健康有益）、help retain something（有助於保留某物）、be dried but not fermented（經乾燥但未發酵）、a possible allergic reaction（可能的過敏反應）。
What is so special about green tea? The Chinese and Indians 16 it for at least 4,000 years to treat everything from headache to depression. Researchers at recently concluded that a compound in green tea 17 the growth of cancer cells. Green tea is also helpful 18 infection and damaged immune function. The secret power of green tea is its richness in a powerful anti-oxidant.
Green tea and black tea come from the same plant. Their 19 is in the processing. Green tea is dried but not fermented, and this shorter processing gives it a lighter flavor than black tea. It also helps retain the tea's beneficial chemicals. That is 20 green tea is so good for health.
The only reported negative effect of drinking green tea is a possible allergic reaction and insomnia due to the caffeine it contains.