这种火箭使用固体燃料作为推进剂。

This rocket uses solid fuel as its ___propellant.

这种喷雾杀虫剂使用压缩气体作为推进剂。

This insect spray uses compressed gas as the ___propellant.

好奇心是推动她学习新技能的动力。

Curiosity was the ___propellant behind her learning new skills.