The palace is heavily guarded, because inside its walls ________.[ ]

A. where sit the European leaders      

B. the European leaders there sit

C. sit the European leaders          

D. that the European leaders sit

以下属于专业技术人员必须学习和掌握的科学素养的是（）科学素养。

A.普遍

B.方法论

C.技术

D.专业