他一时冲动买下了那辆昂贵的跑车。
He bought the expensive sports car on ___impulse.
电脉冲触发了肌肉收缩。
The electrical ___impulse triggered the muscle contraction.
她一时冲动买下了那条昂贵的项链。
She bought the expensive necklace on a sudden ___impulse.