The idea was developed when a Spanish designer travelling to the Philippines observed a traditional Filipino shirt 22 together with the fibers of pineapple leaves.
答案：(C) woven
過去分詞 woven 作補語，被動語意「被編織在一起」（襯衫是用鳳梨葉纖維編織而成的）；wove（過去式，這裡需要分詞不是限定動詞）、weaving（現在分詞，主動語意方向不合）、to weave（不定詞）都不合。
看到 observed 後面接了 a traditional Filipino shirt，你可能直覺選 wove，覺得要用動詞。先數一下這個子句已經有幾個動詞：when 引導的子句主詞是 a Spanish designer，動詞是 observed，限定動詞已經有了，空格不能再放一個。
這是國中句型的長大版。你學過 see sb do 和 see sb doing：I saw him cross the street.（我看到他穿越馬路，強調整個過程）、I saw him crossing the street.（我看到他正在穿越）。observe 和 see、hear、watch、notice 是同一類，除了原形動詞和現在分詞，還有第三種：受詞後面接過去分詞，表示「受詞被……」。例如 We saw Nelson Mandela presented with a special prize.（我們看到曼德拉被頒發特別獎）（例句出自劍橋 English Grammar Today）。這一格也一樣：shirt 是被編織的，不是自己去編織別人，所以用過去分詞 woven。還原成完整子句就更清楚：she observed that a traditional Filipino shirt was woven together with the fibers of pineapple leaves.（她注意到一件傳統菲律賓襯衫是用鳳梨葉的纖維編織在一起的）。另外 weave 是不規則動詞，三態為 weave–wove–woven，過去分詞是 woven 不是 weaved，字形本身就是這一格的考點之一。
wove 是過去式，屬於限定動詞，這個位置已經有 observed，再放一個會變成一個子句裡有兩個動詞。weaving 是現在分詞，語意會變成襯衫主動在編織別的東西，方向不合。to weave 是不定詞，這類感官動詞的受詞補語不接 to V，就像我們說 I saw him cross，不會說 I saw him to cross。
observe／see／hear／watch／notice + O + Vpp（看到、聽到某物被……）、weave–wove–woven（編織，三態變化）、be woven together（被編織在一起）、be made of／from（由……製成）、the fibers of（……的纖維）、travel to（前往……）。
The pineapple, a delicious tropical fruit, has been valued for centuries not only for its distinct and unique taste, but also for its miraculous health and medical benefits. But pineapples can also be a fashionable fruit: Pineapple leaves can 21 a substitute for leather.
The idea was developed when a Spanish designer travelling to the Philippines observed a traditional Filipino shirt 22 together with the fibers of pineapple leaves. After five years of research, she created from pineapple leaves a material which, like real leather, can be used for making bags, shoes, and 23 textile products. It is an eco-friendly and biodegradable fiber.
This eco-friendly leather has clear 24 for the environment, compared to real leather and synthetic leathers. It requires fewer chemicals, making it safer for the workers in factories. Its manufacture also leaves a smaller carbon footprint. In addition, the leftover material following the removal of fibers can even be used as a natural fertilizer back in the pineapple fields. 25 its low cost, this innovative material is already being used by many leading fashion companies to make their products.