If you're writing a one line function, whose sole purpose in life is addition, and, clearly, this is about addition, well, then it's, in fact, A reasonable to use a shorter symbol like A, but I do have to specify it's type.

如果你在写一个一行的函数，它唯一的目的是,做加法，显然这是关于加法的，好的，实际上，用一个短的标识符是合理的，像，但是我必须指明它的类型。

哈佛公开课 - 计算机科学课程节选

There are services now, we don't know yet how to get those stem cells out of cord blood and how to use them for therapies, but it's reasonable to think that we might know about this in 30 years.

现在已经有提供这样的服务了,我们现在还不知道如何从脐带血中,提取这些干细胞并用于治疗,但有理由相信,在未来的30年内我们会知道的

耶鲁公开课 - 生物医学工程探索课程节选