如果多项式 x2-kx+9能用公式法分解因式，那么k的值是（ ）
A：3
B：6
C：±3
D：±6
正四棱锥S-ABCD的高SO=2，底边长AB=2，则异面直线BD和SC之间的距离（ ）
根据句意和汉语注释，写出单词的正确形式。（1）Guangdong is in the ____ (north) part of the city（2）She danced so ____ (beauty) that everyone clapped their hands.（3）Look! Their____ (wife) are waving to them（4）Do you think noise ____ (pollute) is a terrible problem?
清朝前期,我国疆域辽阔。为加强西北边疆的管理,清政府设置了 ( )
