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Read the source and answer the following questions.

The Northern Plain is broadly divided into three sections. The Western part of the Northern Plain is referred to as the Punjab Plains. Formed by the Indus and its tributatries, the larger part of this plain lies in Pakistan. The Indus and its tributaries - the Jhelum, the Chenab, the Ravi, the Beas and the Satluj originate in the Himalaya. This section of the plain is dominated by the doabs. Doab' is made up of two words - 'do' meaning two and 'ab' meaning water. Similarly 'Punjab' is also made up two words -'Punj' meaning five and 'ab' meaning water.

The Ganga plain extends between Ghaggar and Teesta rivers. It is spread over the states of North India, Haryana, Delhi, Uttar Pradesh, Bihar, partly Jharkhand and West Bengal to its East, particularly in Assam lies the Brahmaputra plain. The Northern plains are generally described as flat land with no variations in its relief. It is not true. There vast plains also have diverse relief features. According to the variations in relief features, the Northern plains can be divided into four regions. The rivers, after descending from the mountains deposit pebbles in a narrow belt of about 8 to 16 km in width lying parallel to the slopes of the Shiwaliks. It is known as bhabar. All the streams disappear in this bhabar belt. South of this belt, the streams and rivers re-emerge and create a wet, swampy and marshy region known as Terai. This was a thickly forested region full of wildlife. The forests have been cleared to create agricultural land and to settle migrants from Pakistan after partition.

The fertility of the Northern plain is the result of

A) action of glaciers

B) adequate rainfall

C) its level land

D) depositional work of the rivers