Yes it is, it has a period therefore a complete sentence.
A hook is to catch the readers attention. A hook can be, Chewing gum helps you concentrate for longer, study suggests.
Makes sense i understand why they would do it
the FORMAL meaning of concord is a agreement between people or peace
the GRAMMAR meaning of concord is basically the same thing but with gender, people or basically any other GRAMMATICAL that effects the form of words
Thats a lot of stuff I don't have much time sorry, I know that the action in 18. is Jumped though
