We can never be sure in an observational study of a casual relationship.

我们永远不能肯定是一个因果关系的观察研究。

It started out as just a casual relationship but one day I realized we had fallen in love.

起初我们只是很普通的朋友关系，可后来有一天我忽然意识到我们相爱了。

There is very obvious casual relationship between firm decision behavior rationality and firm performance.

企业决策行为理性与企业绩效有很明显的因果关系。

The effect of this is to substitute fortuitous and casual relationship for the more intimate and permanent associations of the smaller community .

这实际上就是以偶然的、临时的接触关系，代替了小型社区中较亲密的、稳定的人际联系。

The effect of this. is. to substitute fortuitous and casual relationship for the more intimate and permanent associations of the smaller community.

这实际上就是以偶然的、临时的接触关系，代替了小型社区中较亲密的、稳定的人际联系。