— I bought a tie for my father. He loves it.
A:what you did
B:where you went
C:when you shopped
设数列an为等差数列,其前n项和为Sn,已知a1+a4+a7=99,a2+a5+a8=93,若对任意n∈N*都有Sn≤Sk成立,则k的值为( )
在“探究加速度与力、质量的关系”的实验中: