An adjustment refusal message requires your best communication skills 14 it is bad news to the receiver. You have to refuse the claim and retain the customer __15__ .
答案：(C) because
because 表示因果，「因為這是壞消息，所以需要最好的溝通技巧」，符合語意邏輯。till（直到）、unless（除非）、therefore（因此，此處文法上不能直接連接兩個子句作連接詞用）都不符合這裡的因果關係。
四個選項的中文都能說成某種關係，therefore 的「因此」尤其眼熟，你會覺得它擺在這裡也通。
這是邏輯勾環，但要先解決一個形態問題再談語意。空格後面是 it is bad news to the receiver，一個完整的子句，所以空格要的是連接詞，不是副詞——therefore 是連接副詞，它可以出現在副詞能出現的位置，卻不能拿來把兩個子句接起來（劍橋 English Grammar Today）。這一步就刷掉一個。再看語意：前半是「拒絕調整的信最需要你的溝通技巧」，後半是「因為對收信的人來說這是壞消息」——後面那一句正是前面那一句的原因，所以用 because。填進去讀成 requires your best communication skills because it is bad news to the receiver。
till（直到……為止）標示的是時間的終點，兩件事之間不是時間關係；unless（除非）等於 if...not，會變成「除非這是壞消息，否則就需要溝通技巧」，與整段的意思剛好相反；therefore 是副詞，就算語意勉強讀得通，也不能單獨用來連接兩個子句。
because ＋ 子句（因為，連接詞）、because of ＋ 名詞（因為，後面接名詞）、therefore（因此，連接副詞）、unless（除非，等於 if...not）、bad news（壞消息）、communication skills（溝通技巧）。
Handling customer claims is a common task for most business firms. These claims include requests to exchange merchandise, requests for refunds, requests that work 11, and other requests for adjustments. Most of these claims are approved because they are legitimate.
However, some requests for adjustment must be 12, and an adjustment refusal message must be sent. Adjustment refusals are negative messages for the customer. They are necessary when the customer is 13 or when the vendor has done all that can reasonably or legally be expected.
An adjustment refusal message requires your best communication skills 14 it is bad news to the receiver. You have to refuse the claim and retain the customer 15. You may refuse the request for adjustment and even try to sell the customer more merchandise or service. All this is happening when the customer is probably angry, disappointed, or inconvenienced.