Answer:
It depends, though I think it is NOT THAT EASY. If you are logged into your school account on your personal device and also logged into the browser with your school account, they will be able to track your activity. That being said, your school will not have access to your personal account search history.
There is no way to define the 'best' site. Each site offers a unique experience along with the fact it might not display the same information as the other ones. The APEX site (As far as I know, it is a school test site) Won't really be able to help unless you are willing to do a few tests. I would go for Scholarshipexperts.com
The answer is : Cache. It is a small amount of memory stored on the central processor for easy access. Cache is where active data are placed for easier access, it stores recently used information so that it can be quickly accessed at a later time. Some types of cache are browser cache, disk cache, memory cache, and processor cache.