The correct answer is C. Prithvi is a surface-to-surface missile developed by the Defence Research and Development Organisation (DRDO) of India. It is a short-range ballistic missile (SRBM) with a range of 150 to 350 kilometres. The missile is named after the Hindu god of the earth.
Prithvi was first test-fired in 1988 and inducted into the Indian Army in 1994. It is used to defend large installations like oil-fields, power plants, and other strategic assets against enemy attacks. The missile can be launched from a mobile launcher and is capable of carrying a nuclear warhead.
Option A is incorrect because Prithvi is not used to test the performance of an indigenously built heat-shield. The heat-shield is a component of the missile that protects it from the heat generated during re-entry into the atmosphere. The heat-shield is not indigenously built, but is imported from Russia.
Option B is incorrect because Prithvi can hit targets without the help of the Air Forces. The missile is capable of being launched from a mobile launcher and can reach its target without the need for air support.
Option D is incorrect because Prithvi is a surface-to-surface missile. It is not a surface-to-air missile.