Which of the Following Statements Is True of the Kyoto

Which of the following statements is true of the Kyoto Protocol?

A) It called for a 50 percent reduction from 1990 levels of greenhouse gas emissions to be achieved by 2010.
B) It became binding when ratified by 180 countries,on Russia's ratification in late 2004.
C) It was ratified first by the United States.
D) It acknowledged that underdeveloped countries were principally responsible for the greenhouse gas levels at that time.