During those three to four months of use, there are several ways to keep a toothbrush clean. 14 , rinse your toothbrush thoroughly with tap water after use, making sure to remove any toothpaste and debris.
答案：(D) For example
【轉折語】前句提到「有幾種方法可以保持牙刷清潔」，後句舉出具體做法（沖洗牙刷），故用 For example（舉例）承接。In short（簡言之）、Otherwise（否則）、Nevertheless（然而）皆不符合舉例語境。
四個選項都是轉承語，你知道要看前後兩句的關係，但前一句只是一句總說，後面又跟著好幾個祈使句，一時看不出誰跟誰是什麼關係。
這是邏輯勾環，而且線索一定要跨句才看得到。前一句 there are several ways to keep a toothbrush clean（有好幾種保持牙刷清潔的方法）是一句總說；空格之後 rinse your toothbrush thoroughly with tap water、Store your toothbrush in an upright position、do not share toothbrushes 是一條一條的具體做法。從一句通則走到底下的具體個案，用 For example（舉例來說）。填進去讀成 For example, rinse your toothbrush thoroughly with tap water after use。這一招在克漏字裡很常用：文章若在列清單，先確認空格落在清單的哪個位置，是開頭、中間還是收尾，答案往往就定了。
In short（簡言之）用在把前面講過的內容收攏成一句結論，但空格後面是往下展開不是往回收，方向相反；Nevertheless（儘管如此）要求前後語意有轉折，這裡前後是同一個方向；Otherwise（否則）要求前面先有一個條件或指示、後面講不照做的下場，前一句沒有那個條件。
for example（舉例來說）、in short（簡言之）、nevertheless（儘管如此）、otherwise（否則）、rinse A with B（用 B 沖洗 A）、keep ＋ 受詞 ＋ 形容詞（讓某物保持某個狀態，keep a toothbrush clean）。
Brushing your teeth regularly will help you maintain a healthy smile. But that smile won't last long if you don't take proper care of your toothbrush and switch to a new one often. According to the American Dental Association (ADA), toothbrushes can harbor bacteria. These germs come from the mouth and can 11 in toothbrushes over time.
Many Americans replace their toothbrushes only once or twice a year. The ADA, however, recommends 12 a new toothbrush every three to four months. Children's toothbrushes may need to be changed more 13 .
During those three to four months of use, there are several ways to keep a toothbrush clean. 14 , rinse your toothbrush thoroughly with tap water after use, making sure to remove any toothpaste and debris. Store your toothbrush in an upright position, and let 15 air dry. Most importantly, do not share toothbrushes.