Consider relations Book(name,title) and Nobel(name,category,year), where Book records author name and title of books, and Nobel records winner names, categories, and years of Nobel prizes. The category could be "peace", or "chemistry", for example. From the following expressions (relational algebra or SQL), indicate those that correctly express the query "list the titles of books authored by Nobel prize winners".

	1.	select * from Nobel where name=Book.title
	2.	project[title](Book natural-join Nobel)
	3.	select[category='Nobel'](Book)
	4.	select name from Book natural join Nobel where category=title
	5.	project[title](Book natural-join project[name](Nobel))
	6.	select title from Book, Nobel where Book.name=Nobel.name
	7.	project[title](Book) natural-join project[category](Nobel)