老样子，先看下官方对negative keywords的解释和介绍。
Negative keywords prevent your ads from displaying when a shopper’s search matches your negative keywords. They help you exclude poorly performing searches, reducing your advertising cost and increasing your return on investment (ROI).
You can also use negative keywords to display ads to shoppers you’re primarily interested in reaching. For example, if you’re selling silver jewelry you can display your ads for silver necklaces and not silver plated necklaces by adding the negative keyword phrase "silver plated” to the ad group that runs your ads for silver necklaces.
Negative keywords can be used with phrase and exact match types. You cannot change the match type of an existing negative keyword.
Here are examples of negative keyword match types and the types of shopper searches that will block your ad, as well as those that won’t block your ad.
以及官方给出的一个example list：
下图是我补充的2个示例：
Negative有2种级别：
- Campaign Level （控制同个Campaign下所有的groups keywords）
- Group Level（控制自己group下的keywords）
Note: 无法通过bulk operation操作campaign level negative keywords。
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