What about ____ (go) to the Great Wall for our summer holiday?
fifteen+one=____
(Ⅰ)求f(t)的单调减区间;
(Ⅱ)求证:f(t)+f(t+2)+f(t+4)是定值.
商鞅变法是战国时期最大的变法。他的变法措施中体现了( )