If something happens to a program you are working with on your Mac computer, and you have no choice, you will need to access 'force quit'. This is very easy to do, and luckily on a Mac you probably won't use it very often. There are several ways to do this and this video takes you through all of them. If you can, try and save your information before doing a force quit, because you may not be able to recover changes once the app closes.
If you need to force quit fast and nothing else is working, try this keyboard combination while the application is open:
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