Arrange sentences A, B, C and D between sentences 1 and 6 to form a logical sequence.
1. The process continued for million of years.
A. Tibet, before the collision of the continents, had been a well-watered plain along the southern edge of Asia.
B. Nor has this process stopped.
C. On the site of the ancient sea there flow stood the highest and newest mountains in the-world.
D. It was not only pushed upwards but gradually deprived of its rainfall by the young mountains and so changed into the high cold desert.
6. India is still moving north at the rate of 5 centimetres a year, and each year the rocky summits of the Himalayas are a millimetre higher.