the green one is just another textbook by another publisher. you need to be reading some proper books not the textbook. were you not given a reading list? the absolute must reads on my level 3s are
http://www.amazon.co.uk/gp/product/1...SIN=1444102842
http://www.amazon.co.uk/gp/product/0...SIN=0141039434
http://www.amazon.co.uk/gp/product/0...SIN=0335241565
and this
http://www.amazon.co.uk/Penny-Tasson...3815809&sr=1-1
students who read find the course much easier and they are far higher achieving. the textbook is just an explanation not a book that will enrich you.