--
-- I can jump.
A:How's the weather?
B:What's your name?
C:What can you do?
一For five days.
传染病与非传染病不同的是,传染病具有( )
①传染性 ②广泛性 ③流行性 ④暴发性
已知等差数列{an)的前n项和为Sn=﹣n2+(10+k)n+(k﹣1),则实数k=____ ,an=____