Choose the correct sentence which is built from the words and phrases given:
Its population / estimate / over 3.3 million / 2007 / constantly / grow / due to / become / major metropolitan area / Northern Vietnam.
A. Its population, was estimated over 3.3 million in 2007, is constantly growing due to its becoming a major metropolitan area of Northern Vietnam.
B. Its population, which was estimated over 3.3 million in 2007, is constantly growing due to it is becoming a major metropolitan area of Northern Vietnam.
C. Its population, which was estimated over 3.3 million in 2007, is constantly growing due to its becoming a major metropolitan area of Northern Vietnam.
D. Its population, which estimated over 3.3 million in 2007, is constantly growing due to its becoming a major metropolitan area of Northern Vietnam.