First, free velocity, constant velocity can be obtained for free without doing anything.

首先,速度是无偿的,恒定速度不需外力作用就能无偿获得

耶鲁公开课 - 基础物理课程节选

They are kept track of very closely, but because there's still smallpox that exists on the planet, there is some concern that that could be obtained and used to develop a weapon.

并且科学家们仔细记录病毒的使用情况,但因为这星球上仍存在天花,就会有人担心,某些人会获得天花病毒,并将其制成武器

耶鲁公开课 - 生物医学工程探索课程节选