词汇讲解：
1. gasoline n. 汽油
例句：This car runs 5 miles on a gallon of gasoline.
这部汽车一加仑汽油可以行驶五英里。
2. hover vi. 徘徊;停留
例句：The dogs hovered around me while I was fixing their dinner.
我给狗儿们弄吃的时候它们围着我转。
3. retail n. 零售
例句：The retail dealer buys at wholesale and sells at retail.
零售商批发购进货物, 以零售价卖出。
4. advocacy n. 支持, 拥护, 提倡
例句：He is insistent on the advocacy of new scientific methods.
他坚�
