His parents were worried that he______ too much time chatting on line.
A:spent
B:cost
C:paid
D:had
已知点A(5,m)与点B(n,﹣4)关于原点对称,那么点P(m,n)的坐标是( )
读20元人民币版面图案,该图案所示为我国的桂林山水,该地形景观的主要成因是( )