HeLa cells have gone to the moon to test the effect of zero gravity.

VOA: special.2010.07.21

If you fail to take the test, you get zero, and I average the zero in.

如果你没能参加，那即是零分，我算平均分的时候会加入那个零分。

麻省理工公开课 - 固态化学导论课程节选