The correct answer is C. 720 km.
The Ravi River is a tributary of the Indus River, flowing through the Indian states of Himachal Pradesh and Punjab, and Pakistan. It is the fifth-longest river in Pakistan. The river originates in the Pir Panjal Range in Himachal Pradesh, India, and flows for a total length of 720 kilometers (450 mi) before joining the Indus River near Mithankot in Pakistan. The Ravi River is an important source of irrigation and drinking water for both India and Pakistan. It is also a popular tourist destination, with many historical and religious sites located along its banks.
Option A is incorrect because the length of the Ravi River is about 720 kilometers, not 300 kilometers.
Option B is incorrect because the length of the Ravi River is about 720 kilometers, not 420 kilometers.
Option D is incorrect because the length of the Ravi River is about 720 kilometers, not 900 kilometers.