She felt badly about losing the ring which her parents had given her for her nineteenth A B C D birthday.
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举一反三
【简答题】在数列{a n }中,若a n 2 -a n-1 2 =p(n≥2,n∈N*,p为常数),则{a n }称为“等方差数列”,下列是对“等方差数列”的判断: ①若{a n }为等方差数列,则{a n 2 }是等差数列; ②{(-1) n }是等方差数列; ③若{a n }是等方差数列,则{a kn }(k∈N * ,k为常数)也是等方差数列. 其中正确命题序号为______.