When evaluating a business, mystery shoppers have to follow certain standard procedures to avoid 13 .
答案：(D) personal bias
語意「必須遵循一定的標準程序以避免『個人偏見』」，personal bias（個人偏見）符合，呼應後文提供checklist確保評估一致性的目的；keen competitions（激烈競爭）、financial hardship（財務困難）、racial conflicts（種族衝突）都不合。
四個選項都是名詞片語，你可能哪個認識就選哪個。這一題真正要問的是：神秘客為什麼需要「標準程序」？ 標準程序存在的目的，就是讓不同的人評出來的結果一致，不摻進個人好惡。
線索在下一句：They are often given a checklist that provides directions on what to observe or look out for to ensure consistency（給他們一張檢核表，指示要觀察什麼，以確保一致性）。ensure consistency（確保一致性）就是 avoid personal bias（避免個人偏見）的正面說法，同一件事的一體兩面。選項難分高下時，找文章有沒有把同一個概念換句話講。
keen competitions（激烈競爭）、financial hardship（財務困難）、racial conflicts（種族衝突）都是社會或經濟層面的問題，跟「評分是否客觀一致」無關。這三個放進句子文法都通，但整段完全沒有相關鋪陳。
personal bias（個人偏見）、be biased against sb（對某人有偏見）、avoid Ving（避免做……）、follow procedures（遵循程序）、ensure consistency（確保一致性）、look out for（留意）。
Mystery shoppers are paid consumers who are hired to shop in stores and collect data. They are sent to a wide variety of service-based businesses, including stores, restaurants, and banks—potentially anywhere customers are served. Sometimes referred to as secret shoppers, mystery shoppers 11 regular customers to purchase items, eat in restaurants, make inquiries, or return items.
They grade and report on the quality of products, customer service, and environment of the stores 12 they are assigned. When evaluating a business, mystery shoppers have to follow certain standard procedures to avoid 13 . They are often given a checklist that provides directions on what to observe or look out for to ensure consistency.
Sometimes these shoppers collect data about their "normal" observations, such as cleanliness of the store or timeliness of the service. They may also pretend to be 14 customers, arguing with a salesperson without a good reason.
With the data they collect, mystery shoppers can identify areas for 15 and thereby help enhance the quality of products and services. In this way, these secret shoppers may help a business gain a competitive edge.