Given this information about Vietnam, which country does it share its northern border with?

Context: Vietnam or Viet Nam, officially the Socialist Republic of Vietnam, is a country in Southeast Asia. It is located at the eastern edge of mainland Southeast Asia, with an area of 331,212 square kilometres and population of 99 million, making it the world's fifteenth-most populous country. Vietnam borders China to the north, and Laos and Cambodia to the west. It shares maritime borders with Thailand through the Gulf of Thailand, and the Philippines, Indonesia, and Malaysia through the South China Sea. Its capital is Hanoi and its largest city is Ho Chi Minh City.

Answer: China