These are the pentoses - remember 5' and 3' because that orients you with respect to what direction the molecule is facing.

这些就是戊糖,记住了5'碳和3'碳就能够,帮你确定分子的方向

耶鲁公开课 - 生物医学工程探索课程节选

For most of us, gravity acts this way, defines a vertical direction very naturally and the blackboard is oriented this way, so very natural to call that x and call that y and line up our axes.

对我们多数人来说,重力作用下,很自然地确定了竖直方向,而我们的黑板又是这个指向的,所以很自然地定出 x 轴和 y 轴,并标出我们的坐标系

耶鲁公开课 - 基础物理课程节选