No, it can never ever be used in this class. 

Yes, it is highly recommended to use on every single assignment.

Although it is not recommended, it can be used sometimes. But it always needs to be cited. If you copy and paste it, you also need to use quotation marks around those words. 

Sure, it can be used sometimes. But you can't ever copy and paste it; you can only paraphrase it in your own words.