试题题干
Fill in the blank with an item as required.
With an appropriate coordinator or subordinator:
Only 
people have the knowledge of the air quality around them will they change unhealthy behaviors.
参考答案
试题解析
coordinator or subordinator指并列连接词或从属连接词。
"only"引导倒装句，本句缺少引导从句的连接词，根据句意应该是“当···时候”，所以填"when"。
句意：只有当人们了解到周围的空气质量时，他们才会改变不健康的行为。