Environmental issues have undergone changes since the 1970’s.

Since 1970, environmental issues have taken mayor relevance regarding international relations. The first treaties that were signed were a product of regional and national efforts from a certain number of countries. However, the issue took global relevance in June 1992 with the signature of the United Nations Convention on Climate Change during the Earth Summit which was held in Rio de Janeiro. This treaty was further extended by the Kyoto Protocol, which was signed in Japan in December 1997.

answer; /// i believe that the correct answer is (d)the huang he river valley;