Which of the following statement(s) is/are found to be correct? I. Formed by the valleys of the rivers Ganga and Brahmaputra, and their tributaries, the Indo-Gangetic plain is about 2,500 km. long and its width ranges between 400 and 600 km. II. Indo-Gangetic Plain occupies one third of India's land surface, forms the most fertile region and are cut off from the south by the Vindhya mountains. III. The plain is a great alluvial crescent, stretching from the Indus River system in Pakistan to the Punjab to the Punjab Plain (in both Pakistan and India) and from the Haryana plain to the delta of the Ganga in Bangladesh where it is called the Padma.