The correct answer is (a). The Himalayan Frontier Thrust (HFT) is a major thrust fault in the Himalayas that separates the Lower Himalaya from the Higher Himalaya. It is a reverse fault, meaning that the lower block has been thrust up over the higher block. The HFT is thought to have formed as a result of the collision of the Indian and Eurasian plates.
The Shivaliks are a mountain range in the northern Indian subcontinent. They are located south of the HFT and are composed of sedimentary rocks that were deposited in a foreland basin during the collision of the Indian and Eurasian plates. The Gangetic Plain is a vast plain in northern India that is located south of the Shivaliks. It is composed of alluvial sediments that were deposited by the Ganges River. The Trans-Himalaya is a mountain range in the northern Indian subcontinent. It is located north of the HFT and is composed of metamorphic and igneous rocks that were formed during the collision of the Indian and Eurasian plates.