Participating nations in the 1997 Kyoto Protocol agreed to reduce overall greenhouse gases emission through 2020 to

A) as much as 20 percent below the levels in the 1990s.
B) as much as 5 percent below the levels in the 1990s.
C) as much as 50 percent below the levels in the 1990s.
D) as much as 50 percent below the levels in the 1960s.