B: Iran is incorrect. Iran is located to the southwest of Pakistan and was also an important hub in the western branches of the Silk Road. However, it does not represent the direct and famous mountainous link from Pakistan to the core eastern regions as China does.
C: Kazakhstan is incorrect. Kazakhstan is a Central Asian country situated far to the north. While it was connected indirectly through other branches of the Silk Road, it does not share a direct, renowned Silk Route border with Pakistan in the same manner as China.