In a way,________global warming is a challenge for man,so we must overcome it to build________fine world.
A:the;/
B:a;the
C:a;/
D:/;a
阅读下列美国钢铁业在某一时期的统计表,从中可以得出这一时期美国钢铁业发展的主要特征是( )
已知0<α<β<π2,且cosαcosβ+sinαsinβ=45,tanβ=43,则tanα=____