Typically, an intensely colored plant has 19 of these protective chemicals than a paler one does.
答案：(A) more
比較級 more...than 固定句型，「顏色越濃的植物，含有的保護性化學物質越多」，符合前文「顏色來自抗氧化物質」的邏輯（顏色濃＝抗氧化物質多）。less 語意相反，most／least 是最高級，不能跟 than 連用。
四個選項都是 much 與 little 的比較級或最高級，形態很近，你會憑中文挑一個。
鑑別度高達 59。先用形態刷一輪：句尾有 than，而 than 只跟比較級搭配，most 與 least 是最高級，一步出局。剩下 more 與 less，這一步句內就分不出來了——空格前是 an intensely colored plant（顏色濃豔的植物），than 後面是 a paler one（顏色較淡的），但顏色濃到底代表那些化學物質多還是少，這一句自己沒有講。要回到前面那句主題句：The colors come mainly from chemicals known as antioxidants（這些顏色主要來自被稱為抗氧化物質的化學物質）。顏色既然是那些物質造出來的，顏色越濃就代表物質越多，所以填 more。填進去讀成 has more of these protective chemicals than a paler one does。另外留意句尾那個 does：它代替的是前面整串 has ... of these protective chemicals，免得同樣的話再說一次。這與國中學過的 Do you like it?—Yes, I do. 是同一件事，用助動詞把重複的部分頂掉。比較句的句尾常常就掛著這樣一個 does、did 或 is，看到它先問一句「它在代替前面哪一串」，句子的骨幹就清楚了。
less 方向剛好相反；most 與 least 是最高級，不能與 than 連用，而且最高級前面通常要有 the。
more of ＋ 名詞 ... than（比……有更多的）、the ＋ 最高級（最……的，不與 than 連用）、than ＋ 主詞 ＋ does（助動詞代替前面重複的動詞部分）、intensely colored（顏色濃豔的）、pale（顏色淡的、蒼白的）、protective（保護性的）。
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.