题目

. ------ The door was open. ----- It ___________open. I had locked it myself and the key was in my pocket.        A. can’t be      B. mustn’t be       C. can’t have been       D. mustn’t have been 答案：C判断下列各组中的两个函数是同一函数的为（ ）A．f（x）=B．f（x）=x，g（x）=C．f（x）=，g（x）=D．f（x）=x，g（x）=（）2