That is, after he 16 his pages in the hymn book with small bits of paper, the small pieces would invariably fall out all over the floor.
答案：(A) marked
語意「用小紙片標記聖歌本的頁面」，marked（標記）符合這個「用紙片做記號」的行為；tore（撕）、served（服務）、took（拿）都不符合這個語境。
mark 這個字，你腦中第一個浮現的多半是名詞「分數、記號」，或是 marker（麥克筆）。所以看到空格後面接的是 his pages in the hymn book with small bits of paper，你會很想挑一個動作感更強的字，這一格只有五成的人答對，卡點就在沒把 mark 當動詞用。mark 當及物動詞是「做記號、標示」，最常用的句型是 mark A with B（用 B 在 A 上做記號）。
還原成完整句子：after he marked his pages in the hymn book with small bits of paper（他用小紙片在聖歌本的頁面上做記號之後）。判斷關鍵是 with small bits of paper 這個介系詞片語，它交代的是「用什麼工具」，前面的動詞就必須是「拿工具去做某件事」的動作。同一篇後面出現的 a good bookmark（很好的書籤）是最直接的篇內對照：bookmark ＝ book ＋ mark，書籤的功能正是在書上做記號，作者前後是刻意呼應的。
tore 是 tear（撕）的過去式，「撕書頁」與後文不合——掉滿地的是 the small pieces（那些小紙片），不是被撕破的書頁。served 的受詞通常是人或食物（serve customers 服務顧客、serve dinner 上菜），接 pages 不通。took 只是「拿」，take his pages with small bits of paper 說不出「標記」的意思。
mark A with B（用 B 在 A 上做記號）、a bookmark（書籤）、bits of paper（小紙片、紙屑）、fall out（掉出來、脫落）、all over the floor（掉得滿地都是）、tear a page out of a book（把一頁從書裡撕下來）
Art Fry was a researcher in the 3M Company. He was bothered by a small irritation every Sunday as he sang in the church choir. That is, after he 16 his pages in the hymn book with small bits of paper, the small pieces would invariably fall out all over the floor.
One day, an idea 17 Art Fry. He remembered a kind of glue developed by a colleague that everyone thought 18 a failure because it did not stick very well. He then coated the glue on a paper sample and found that it was not only a good bookmark, but it was great for writing notes. It would stay in place 19 you wanted it to. Then you could remove it 20 damage.
The resulting product was called the Post-it, one of 3M's most successful office products.