Correct Answer:
C. 600 km
The question asks for the approximate length of the border between Pakistan and China. 600 km is the correct approximate length. The border, primarily traversing the challenging Karakoram mountain range, is officially measured at approximately 596 kilometers, which is commonly rounded to 600 km.
- 400 km and 500 km are significantly shorter than the actual length of the border.
- None of these is incorrect because 600 km is a widely accepted approximation for the border's length.
This border is strategically important for both nations, facilitating trade and regional connectivity.