To expand on #3...enterprise, company, and firm. They are all definitely synonyms but I would not use them all equally. Enterprise in the United States is actually a car rental business name so I think most people mostly associate enterprise with that company specifically. Company is used pretty commonly as another word for business but typically means that it is more established, or larger than some other businesses. The word firm is typically used when talking about a business for lawyers.

It's "What is the difference?" not "What is the different?". "Different" is an adjective, not a noun.

1. to insist is to really push someone to do something, assert is to state something with force 2. ample, abundant, and plentiful are synonyms so they all mean pretty much the same thing 3. entireprise, company, and firm are also synonyms