Có is to used to form a question. For example: Bạn có khoẻ không (Are you healthy?), Tôi khoể (I am healthy).
alfredo_555 is correct. I would also like to add that you could omit the có in this sentence. It would still make sense, but it is more proper if you kept the có.
Using "the" implies that we are referring to a specific patch of grass or a specific kind of grass. Without the article "the", we are referring to grass in general.
So, from what I unlearned in this series of lessons is I would be marked wrong for using các. Các good for elephants but not architects, apparently. I used to think they were equivalent until marked wrong for using những for architects.