boster

例句：

1. 1.The new vaccine is a booster against the flu.
   新疫苗是对抗流感的增强剂。
2. 2. The teacher was a booster for her students' success.
   老师是学生们成功的激励者。
3. 3. The new drug is a stimulant to improve memory.
   新药是提高记忆力的刺激物。