We're already using it up in this pi bond here, so that means we're limited to only two other spots on the molecule, so we have three.

我们已经把它用到这个π键里去了，所以这意味着,我们在分子里只剩下两个位置，所以一共是三个。

麻省理工公开课 - 化学原理课程节选

The seconds cross out, the kilograms cross out, one of the meters crosses out from the top, so we're left with an answer in meters.

秒消掉了，千克消掉了，单位米和上面的一起约去了，所以我们得到的答案只剩下米。

麻省理工公开课 - 化学原理课程节选