They asked for a ransom of $2,000 to return the boy. 16 , their plan quickly got out of control.
答案：(A) However
前文描述綁匪精心策劃綁架計畫、原本預期一切順利，這句「然而」轉折，計畫卻很快失控了，However（然而）符合這種「預期順利卻事與願違」的對比轉折；Accordingly（因此/於是）表順接因果，會變成「因為計畫了綁架，於是計畫就失控」，因果邏輯不通；Otherwise（否則）、Furthermore（此外）都不合。
However 你早就背過「然而」，這一格對多數人不難，但仍有一群人會挑 Accordingly，原因是前一句剛講完綁匪「藏好人、開價 $2,000 要贖金」，讀起來像一連串動作正往下推，於是順手填了「於是、因此」。空格在句首、後面接逗號，這個位置放的是連接副詞（linking adjunct），它唯一的工作就是標示「這一句和前一句是什麼關係」（劍橋 English Grammar Today），所以判斷的依據不在這一句裡面，一定要往回讀一句。
把前後兩句並排看：前一句是綁匪的「計畫」（藏人、開價 $2,000 要贖金），後一句是 their plan quickly got out of control（他們的計畫很快就失控了）。計畫周全 vs 立刻失控，是「本來以為會這樣、結果卻那樣」的對比，要用轉折。驗算方式很簡單：試著用 but 把兩句接起來 — They asked for a ransom, but their plan quickly got out of control. 接得起來，就填 however。這裡可以接上你國中就學過的 but：but 是連接詞，把兩個子句接成一句；however 是副詞，前面要用句號或分號斷開，自己後面再加逗號。意思幾乎一樣，標點卻不一樣，這是寫作時最常被扣分的地方。
Accordingly（因此、於是）是順接因果，填進去會變成「因為他們開價要贖金，所以計畫就失控了」— 但開價本身不會導致失控，真正的原因（小孩太皮）要到下一句才登場，因果對不上。Otherwise（否則、不然）需要一個「不這麼做就會如何」的條件，前一句沒有這種假設。Furthermore（此外、而且）是再補一項同方向的訊息，但「計畫失控」不是綁架步驟的追加說明，方向相反。
however（然而）、otherwise（否則、不然）、furthermore（此外、而且）、accordingly（因此、據此）、get out of control（失控）、ask for a ransom（索討贖金）、hold sb for ransom（挾持某人勒贖）、compensate for（彌補……）。
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.