Enzymes consist of various types of proteins that work to drive the chemical reactions 17 for certain types of nutrients to take effect.
答案：(B) required
【過去分詞作形容詞】required 修飾 chemical reactions，表示「（某些營養素生效）所需要的化學反應」，為被動意涵。requires 為限定動詞形式，不可直接修飾名詞；requiring 為主動意涵，語意不合；to require 不定詞不符合此處修飾名詞的句法。
四個選項是 require 的四種形態排在一起，你會直覺認定這是文法題，然後開始想「反應是主動需要，還是被需要」。方向沒錯，但很多人在這裡繞了遠路：句子前面已經有一個 that work to drive… 的關係子句，再看到 for certain types of nutrients to take effect 這一長串，很容易讀成「反應需要某些營養素生效」，於是選了主動的 requiring。
先數這一句有幾套主詞與動詞。主要子句是 Enzymes consist of…，關係子句是 that work to drive the chemical reactions，到這裡成分已經滿了；空格後面沒有連接詞、也沒有關係代名詞，所以空格不可能再放一個限定動詞，requires 先出局（何況 reactions 是複數，也對不上 requires）。剩下三個裡，requiring 用同一招刷掉：require 是及物動詞，主動就一定要有受詞，但空格後面直接接 for … to … 這一串，找不到受詞可接。答案是過去分詞 required，還原成完整子句就是 the chemical reactions that are required for certain types of nutrients to take effect（某些營養素要發揮效用所需要的化學反應）。掛鉤是國中的 a boy called Tom：分詞單獨一個的時候放在名詞前面（a broken window），一旦後面還掛著東西，整串就得移到名詞後面。答對率四成一，鑑別度只有 24，吃虧的反而是文法練得熟的人：required 的意義主詞是 reactions，而 for certain types of nutrients 是 to take effect 的意義主詞，兩層意義主詞疊在一起，越是仔細去分主動被動，越容易把這兩層讀混。
requires 是限定動詞形式，前面沒有連接詞可以再帶一個子句，主詞單複數也對不上。requiring 是主動，後面缺受詞。to require 當後位修飾（postmodifier）時帶有「將要、有待」的意味（the reactions to require attention 指還沒被處理的反應），與本句「已經是必需的」對不上，而且同樣是主動、同樣缺受詞。
be required for（為…所必需）、take effect（生效、發揮效用）、consist of（由…組成）、drive a reaction（推動反應）、speed up（加快）、either A or B（不是 A 就是 B）
One factor that separates a living thing from an inanimate object is the organism's ability to carry out chemical reactions that are crucial for its survival. Imagine the infinite amount of reactions that a large organism such as human carries out every single day. 16 of these reactions are possible without enzymes.
Enzymes consist of various types of proteins that work to drive the chemical reactions 17 for certain types of nutrients to take effect. Enzymes can either launch a reaction or speed it up. In the absence of enzymes, reactants may take hundreds of years to convert into a usable product, if they are able to do so 18 . This is why enzymes are crucial in the sustenance of life on earth.
Enzymes, 19 , do not always function perfectly. In 1902 Sir Archibald Garrod was the first to attribute a 20 to an enzyme defect, which he later referred to as an "inborn error of metabolism." Today, newborns are routinely screened for certain enzyme defects such as PKU (phenylketonuria) and galactosemia, an error in the handling of the sugar galactose.