A:held; was interested
B:hold; was interested
C:should hold ; be interested
D:should hold ; interested
西北地区划分的主导因素是( )
远距离输电时,为了减少输电线上电能损失,应( )
已知函数f(x)=log3x,x>02x,x≤0,则ff(19)的值为____