概括段意并补全句子：In the twentieth century, soot________Aproduces much more global warming than a

In the twentieth century, soot________

A

produces much more global warming than a carbon-dioxide forcing of the same magnitude

B

contributed to 25 percent of observed global warming

C

winter and spring

D

the warming effects increase

E

still surpass soot warming the world's climate during the last century

F

can be seen mostly in the Northern Hemisphere