Livemocha. com is a free site ________ visitors can not just learn various languages but also chat online. A.where B.which C.that D.what 答案:A 先行词为a free site,空格处在定语从句中作状语,因此应用关系副词where。 已知函数f(x)=2(ln1+x+12x2)-ax,其中a为常数.(Ⅰ)若f(x)在(0,1)上单调递增,求实数a的取值范围;(Ⅱ)求证:Dnk=2k-1k2<lnn+12.