Thanks all for your reply, I still do not understand the concept..(How the grammar rules works.) Some people say: - a 12 week course, 12 weeks course, 12 week course... I am confused. Can anyone please tell what the grammar rule is and how to identify which one I need to apply? Please explain using examples. Also please tell me, how can I identify, a word in a sentence is noun or adjective phrase? any simple technique? for example : We spent three months in France .. in this sentence how I know three months is noun or adjective phrase?