劳动合同是劳动者和用人单位确立劳动关系，明确双方权利和义务的协议。( )
参考答案：对
计算：（-a2）3+（-a3）2=______．
Though great progress has been made in astronomy in the past fifty years, ______ still much that
remains mysterious to astronomers _______ the universe, even the solar system. [ ]
A. It is; of
B. there is; about
C. It is; with
D. there is; with
