Peace and development remain the permanent themes of our times, _____ the world we live in is anything

but quiet. [ ]

A. and

B. if

C. so

D. but

我国四大地理区域中南方地区与北方地区分界线的划分依据是       ，北方地区与西北地区分界线的划分依据是       ，青藏地区与南方地区、北方地区、西北地区分界线的划分依据是         。