现阶段中俄关系的主要特点是 [ ]
A.同盟关系
B.竞争伙伴关系
C.战略协作伙伴关系
D.建设性合作关系
C
The reason why people carry umbrellas in hot summer days is that____to strong sunlight may be
harmful to the skin. [ ]
A. contributing
B. exposing
C. contributed
D. being exposed
公差不为零的等差数列{an}中,a12+a72=a32+a92,记{an}前n项和为Sn.其中S8=8,则{an}的通项公式为an=______.