When he found her, he said, "I know how valuable this stone is, but I'm giving it back to you, 24 that you can give me something even more precious.
答案：(B) hoping
現在分詞片語 hoping，補充說明說話者的心理狀態/目的「希望你能給我更珍貴的東西」；hope（原形動詞，不能這樣單獨補充說明）、hoped（過去式）、to hope（不定詞，不太符合這裡補充說明的伴隨動作語境）都不合。
hope 是你很早就學會的動詞，一看到它就想幫它找主詞，於是把 hope 或 hoped 填進去，讀成「我把石頭還你、我希望……」。問題是這一句已經有主詞和動詞了（I'm giving），逗號後面不能再放一個並列的動詞卻不加連接詞。
先數句子的結構：I'm giving it back to you 是完整的主要子句；逗號後面這一串既沒有自己的主詞，也沒有連接詞。這種位置要放動詞，動詞就得換成分詞形式，用現在分詞片語補充說明主詞當下的心情或伴隨的狀態（劍橋 English Grammar Today 的 -ing clause）。還原成兩句驗算：I'm giving it back to you. ＋ I hope that you can give me something even more precious.（我要把它還給你。我希望你能給我更珍貴的東西。）把第二句的主詞 I 拿掉、動詞改成 hoping，就是原句。這個結構你國中見過最短的版本：While (he was) walking home, he met an old friend.——主詞與前面相同時就省略，動詞改成 V-ing。
hope：原形動詞不能沒有連接詞就直接接在一個完整的句子後面。hoped：過去式，同樣的結構問題還在，而且時間也不對，說話者是此刻抱著希望，不是過去。to hope：不定詞放在這個位置通常表示目的，還原出來會變成「我把石頭還你，是為了希望你給我更珍貴的東西」——希望是心裡的狀態，不是可以刻意去執行的動作，當目的講不通；真要表達這層意思，英文會說 in the hope that...（懷著……的希望）。
hoping that...（希望……，現在分詞補充說明心情）、in the hope that...（懷著……的希望）、give something back to somebody（把某物還給某人）、something even more precious（更珍貴的東西）、know how valuable something is（知道某物有多珍貴）、teach somebody something（教某人某事）。
A wise woman traveling in the mountains found a precious stone. The next day she met another traveler who was hungry. The wise woman generously opened her bag to 21 her food with the traveler. When the hungry traveler saw the precious stone, he asked her to give it to him. The woman did 22 without hesitation. The traveler left, rejoicing.
If he sold the stone, he thought, he 23 enough money for the rest of his life. But in a few days he came back to find the woman. When he found her, he said, "I know how valuable this stone is, but I'm giving it back to you, 24 that you can give me something even more precious. You gave me the stone without asking for anything 25 . Please teach me what you have in your heart that makes you so generous."