题目

.Such an effort_____ the severe snow disaster didn’t prevent the whole nation from celebrating the traditional Chinese New Year happily. A. as the Chinese government has made B. has the Chinese government made that C. the Chinese government has made that D. has the Chinese government made as 答案：B 给出定义：若函数f(x)在D上可导，即f ′(x)存在，且导函数f ′(x)在D上也可导，则称f(x)在D上存在二阶导函数，记f″(x)＝(f ′(x))′.若f″(x)<0在D上恒成立，则称f(x)在D上为凸函数．以下四个函数在(0，)上不是凸函数的是________(把你认为正确的序号都填上)． ①f(x)＝sinx＋cosx;  ②f(x)＝lnx－2x； ③f(x)＝－x3＋2x－1;  ④f(x)＝xex.