许多运动员在训练前会服用一些天然兴奋剂来提高表现。

Many athletes take natural ___stimulators before training to enhance their performance.

医生使用神经刺激器帮助病人恢复手部运动功能。

The doctor used nerve ___stimulators to help the patient regain hand movement.

阳光和水分是植物生长的天然促进剂。

Sunlight and water are natural ___stimulators for plant growth.