北魏孝文帝主动推行汉化政策的实质是
A:提高少数民族素质
B:缓和与汉族地主的冲突
C:适应农耕文化的需要
D:抵御北方游牧民族侵扰
People say it is Canada's most beautiful city, ____(包围)by mountains and the Pacific Ocean.