The knee jerk is a typical respondent.

膝反射是一种典型反射。

It's impossible to say hello without smiling. One leads to the other just as a tap causes a knee jerk.

说“你好”的时候，是不可能不面带微笑的，而且能一个传给另一个，正如敲击膝盖引起的条件反射。

This article suggests a research and production of a simulant electric teaching aid in accordance with the physiology process of knee jerk.

本文根据膝跳反射的生理过程，研制了一个电动模拟教具。

Because we cannot or do not know how to trust in ourselves, we constantly live in a state of fear and worry (which is part of the reason we have knee jerk reactions).

因为不懂得怎样信任自己，我们常常会处于一种担惊受怕和焦愁忧虑的状态，而这实际上也是“膝反应”的一个诱因。

It was a knee-jerk reaction on her part.

这是她未加思索做出的反应。