Is the group of words a sentence or a run-on sentence?   the squirrel climbed onto our deck it filled each cheek with nuts.   a. sentence   b. run-on

Hello!

This is a run-on. 

This is considered a run-on because there are two independent clauses (groups of words that could stand alone as individual sentences) that are not correctly combined. 

The two independent clauses are:
The squirrel climbed onto our deck. It filled each cheek with nuts. 

In order to make this a proper sentence, you would need to add a conjunction:
The squirrel climbed onto our deck and it filled each cheek with nuts. 

I hope this helps you!

Run on. (My question got deleted for some reason)