For now, just know that different kinds of cells, one of the ways they're different is that they express different proteins and the population of proteins on the surface of different cells is different.

现在,你们只要知道有不同的细胞,它们之间的一种区别,就是它们表达不同的蛋白,而不同细胞表面的蛋白种类,也是不同的

耶鲁公开课 - 生物医学工程探索课程节选

it's very difficult when one is so articulate and is able to express exactly what you want to say,

当一个人已经熟谙一门语言，能够用这门语言清楚明白地表达意思，

想学好英语吗？ - SpeakingMax英语口语达人