____ ____ you have?
Andreas Kern and Paul Cibis are famous artists from ____(德国).
已知等差数列{an}的前n项和为Sn,若=a1+a2011,且A、B、C三点共线(O为该直线外一点),则S2011= ( )
下列俗语或成语与物质的化学性质无关的是( )