In addtion,I have to tell you a truth. A person's English level does not depend on whether he has been abroad or not before.Previously, I communicated with several of my friends who studied in US or UK on the internet. Unfortunately I found their language level didn't improve much though they had been abroad for a long period. There are many reasons for this phenomenon. Actually, you know, in linguistics study ,many scholars have concentrated on Second Language Acquisition (SLA) in recent years. Maybe relevant studies on SLA could throw a light on the causes of this phenomenan.