Yet, knowing perfectly well 19 a troublemaker his son was, the father refused to give them any money. 20 , he asked the kidnappers to pay him $250 to take the boy back.
答案：(D) what
【句型】what a + 形容詞 + 名詞 固定感嘆句結構，what a troublemaker his son was（他兒子是多麼一個麻煩製造者），作 knowing 的受詞子句；how（通常接形容詞/副詞本身，不接這種名詞結構）、that、why 都不合。
看到 knowing perfectly well 後面接空格，直覺會填 that，因為「知道……這件事」平常就是 know that。也有很多人挑 how，因為中文說「知道他兒子有多麻煩」，那個「多」讓人反射性想到 how。這一格答對率只有 52%，兩個直覺各拉走一票。
判斷點只有一個：空格後面緊跟著 a troublemaker，是「冠詞 + 名詞」的名詞片語。感嘆句（exclamative）只有兩種開頭，劍橋 English Grammar Today 的「Exclamations」條寫得很清楚：what 後面接名詞片語（What an amazing car!），how 後面接形容詞或副詞（How interesting it was to hear her story!）。這裡後面是名詞，就只能用 what。把句子還原一次會更踏實：直述句是 His son was a real troublemaker.（他兒子真是個麻煩精。）改成感嘆句就是 What a troublemaker his son was!（他兒子是多大的一個麻煩精啊！）本題只是把這整個感嘆句放進 knowing 後面當受詞，所以主詞動詞維持 his son was 的正常順序，不倒裝。想用 how 也不是不行，但整句必須改寫成 knowing perfectly well how troublesome his son was — 名詞 troublemaker 得換成形容詞 troublesome，how 才站得住。what a + 名詞 對上 how + 形容詞，這一組互換請一起記。
that 帶出的名詞子句必須是完整的直述句，也就是 knowing perfectly well that his son was a troublemaker — 文法沒錯，但語序和空格後面的 a troublemaker his son was 對不上，代進去讀就會發現多出一個 a troublemaker。why（為什麼）會變成「知道他兒子為什麼是個麻煩精」，文章沒有在追究原因。how 如上所述，後面得接形容詞或副詞。
What a/an + 形容詞 + 名詞 + 主詞 + 動詞（多麼……啊）、How + 形容詞或副詞 + 主詞 + 動詞（多麼……啊）、know perfectly well（心知肚明、非常清楚）、a troublemaker（麻煩製造者）、refuse to V（拒絕做……）、give sb money（給某人錢）。
Bill and Sam decided to kidnap the son of a banker to compensate for their business loss. They kidnapped the boy and hid him in a cave. They asked for a ransom of $2,000 to return the boy.
16 , their plan quickly got out of control. Their young captive 17 to be a mischievous boy. He viewed the kidnapping as a wonderful camping trip. He demanded that his kidnappers play tiring games with him, such as riding Bill as a horse for nine miles. Bill and Sam were soon desperate and decided to 18 the little terror. They lowered the price to $1,500.
Yet, knowing perfectly well 19 a troublemaker his son was, the father refused to give them any money. 20 , he asked the kidnappers to pay him $250 to take the boy back. To persuade the boy to return home, Bill and Sam had to tell him that his father was taking him bear-hunting. The kidnappers finally handed over the boy and $250 to the banker and fled town as quickly as they could.