There were lots of activities you could to take up (去掉TO ）为什么

There were lots of activities you could to take up (去掉TO ）为什么
There were lots of activities you could to take up (去掉TO ）为什么

There were lots of activities you could to take up (去掉TO ）为什么
去掉to 是因为前面有情态动词could.情态动词后接动原.

情态动词后面紧跟动词原型

could 是情态动词、后直接跟动词原形、不用加to 、