They were not hot enough -- like stars-- to give off light.

VOA: special.2009.04.29

Well, we can't guarantee with UV light we'll have enough energy to eject every single electron, so that's why when we use x-rays, they're higher energy, you can pretty much be guaranteed we're going to eject all of those electrons there.

好，我们不能保证紫外光有足够的能量,激发出每一个电子，所以我们要使用，X，射线，它的能量更高，你可以非常确定,我们可以激发出其中所有的电子。

麻省理工公开课 - 化学原理课程节选

And every night, late at night, I turned the lock of his door and opened it C oh,so gently! And then, when I had made an opening big enough for my head, I put in a dark lantern, all closed that no light shone out, and then I stuck in my head.

VOA: special.2009.05.16

The soldiers and marines quickly realized the light-weight Humvees did not have enough protection against the bombs, so they added some armor.

VOA: standard.2009.11.02