你好，请问这里的happens因为三单才加的s吗？

Question

Something dirty can cause redness and it will make you feel uncomfortable., it is bad for your eyes too
if this happens, the best way is to clean your eyes by using cold water.

Answer 1

是的。if this happens是条件状语从句的谓语，而且是一般现在时的三单形式。

Answer 2

你的理解是对的, if this happens是条件状语从句, 主语是第三人称单数this, 所以动词用三单。 this指前面提到的
something dirty causes redness and
it is bad for your eyes. 请采纳本回答被网友采纳

Answer 3

是的，在if条件从句中this主语是三单，所以用happens

Answer 4

happens 这里加s,是因为一般现在时，主语是单数this，谓语需要用单数。

Answer 5

是的，单数第三人称。
this (thing) happens,...
this (event) happens,...