The birdwatchers, a noun is a person place or thing
I can only answer question 1.
1: One event that relates to this is when British soldiers shot upon colonial revolutionists. This lead to the American Revolution.
Claudius gives Laertes two reasons why he didn't punish Hamlet yet - he says he loves his mother and that the public loves him. So I guess your answers would be Gertrude loves Hamlet and the King does not want to hurt her and the Danes like Hamlet.
These two options are definitely correct, but if you need another one, then maybe also choose The Danes may not believe Claudius too (however, I am unsure about this one because in the text he only states two reasons).
It's when you have too much nutrients in a lake or pond mainly from runoff in big rain storms, this can cause plants to grow more than normal and kill the fish in it for lack of oxygen.
