Which one of the following is the correct percentage of the two (out of the total of 4) greenhouse gases that contribute to the total global warming ?

Question

( A ) $CO_2$ 40%, CFCs 30%
( B ) Methane 20%, $N_2O$ 18%
( C ) $N_2O$ 6%, $CO_2$ 86%
( D ) CFCs 14%, Methane 20%