Research shows that the substances 17 these colors actually protect plants from chemical damage.
答案：(D) responsible for
be responsible for 在此是「造成、導致」而非「負責」：造成這些顏色的物質其實能保護植物免於化學傷害；capable of（有能力）、different from（不同於）、inferior to（劣於）語意都不合。
be responsible for 你只學過「對…負責」（You are responsible for your own safety.），主詞通常是人。用在事物上時意思會轉成「造成、導致」——主詞是原因、for 後面是結果：Smoking is responsible for many deaths.（吸菸造成許多死亡。）
先抓主詞與動詞。這一句的主詞是 the substances，主要動詞是後面的 protect，空格連同 these colors 夾在中間，是修飾 the substances 的一段話，等於省略了 which are。看出這一點很重要——不少人會把空格當成主要動詞的位置，結果整句讀不動。確定它是修飾語之後，四個選項都是「形容詞 + 介系詞」，都能後位修飾，句法一樣篩不出答案，仍要靠語意。線索在下一句：The colors come mainly from chemicals known as antioxidants.（這些顏色主要來自抗氧化劑。）come from 與 be responsible for 講的是同一件事，一個從結果往回看、一個從原因往前看。驗算法：把修飾語還原成完整的關係子句唸一遍——the substances which are responsible for these colors（造成這些顏色的那些物質），再接回 protect plants from chemical damage，整句站得住。
三個都是「形容詞 + 介系詞」，錯的地方不同。be capable of 是「有能力做…」，of 後面要接動名詞或表示能力的名詞，接 these colors 講不通，而且它說的是能力，不是來源。be different from 是「不同於」，會讀成「與這些顏色不同的物質」，但下一句明說顏色就是來自這些化學物質，兩者是同一件事，不是相異的兩件事。be inferior to 是「劣於」，用在比較優劣，物質與顏色之間沒有優劣可比；順帶記同一組的 be superior to（優於）、be senior to（年長於）、be prior to（早於），這一組都用 to 不用 than。
be responsible for（造成；負責）、be to blame for（該為…負責，用於壞事）、account for（說明；占…比例）、result in（導致）、lead to（導致）、be capable of V-ing（有能力做…）、be inferior／superior to（劣於／優於）。
The fruits and vegetables we eat often come in distinctive colors. The rich colors, 16, are not there only to attract attention. They perform another important function for the plants. Research shows that the substances 17 these colors actually protect plants from chemical damage.
The colors come mainly from chemicals known as antioxidants. Plants make antioxidants to protect themselves from the sun's ultraviolet (UV) light, 18 may cause harmful elements to form within the plant cells.
When we eat colorful fruits and vegetables, the coloring chemicals protect us, too. Typically, an intensely colored plant has 19 of these protective chemicals than a paler one does. Research on how chemicals in blueberries affect brain function even suggests that these chemicals may help our own brains work more 20. In other words, eating richly colored fruits and vegetables makes us both healthier and smarter.