Barack Obama, who came into _________ power on January 20, 2009, was awarded _________2009 Nobel Peace Prize.[ ]

A. the; the

B. the; /    

C. /; the

D. /; /

解释气层的孔隙含气饱和度计算公式：Ｓg＝（Ｖg／Ｖep）·100％式中Ｓg；Ｖg；Ｖep各符号的含义及所用单位。