He saw a man with a hole in the leg of his trousers and 29 realized what Californians 30 for the rough work they were doing—good, strong trousers!
答案：(A) needed
整段故事發生在過去（historical narrative），子句裡的動詞需要跟主要敘事時態一致，用簡單過去式 needed，呼應前面的 realized；need（現在式，時態不一致）、needing（不是限定動詞）、have needed（現在完成式，時態不合）都不符合過去式敘事的一致性。
本題大考中心未公布逐題答對率，以下不談數據，只談觀念。
四個選項是 need 的四種形態，你會直覺去想「加州人現在需要什麼」，於是選了現在式。但這一句講的是一八四九年的事，時態要跟整段的敘事對齊。
四個選項都是同一個動詞 need 的形態，可見這一格考的是時態，那就看整段用什麼時態在講。這一篇從頭到尾都是過去的敘事：arrived、was、knew、rushed、took、hoped、saw、realized，全部是過去式。空格所在的子句是 what Californians ___ for the rough work they were doing（加州人做那些粗重的工作時需要什麼）——它掛在主要動詞 realized 底下，時間點與 realized 同時，所以也要用過去式 needed。同一句後面的 they were doing 用的是過去進行式，也印證了整句都在過去。
need：現在式，會變成「他當時領悟到加州人現在需要什麼」，時間線自相矛盾。have needed：現在完成式，時間線的終點在現在，但整段講的是一百多年前的事，接不上。needing：現在分詞，不是限定動詞，而 what 帶出的這個子句需要一個真正的動詞。
realize what sb needs（明白某人需要什麼）、need sth for（為了……而需要）、rough work（粗重的工作）、strong trousers（耐穿的褲子）、what sb was doing（某人當時在做的事）、時態一致（子句要跟主要動詞對齊）。
When Levi Strauss arrived in the United States from Bavaria, he was only seventeen, poor, and knew very 21 English. Like most immigrants, he was 22 a better life. So, when gold was discovered in the West in 1849, he 23 thousands of others and rushed to California.
24 he planned to open a shop in San Francisco, he took many goods with him, 25 a large quantity of canvas. He hoped to sell 26 as material for tents or wagon covers. Business, however, was not 27 he had expected.
28 , as he sat in a cafe in a small town, he had an idea. He saw a man with a hole in the leg of his trousers and 29 realized what Californians 30 for the rough work they were doing—good, strong trousers!