题目

The first use of atomic weapons was in 1945. and their power ______ increased enormously ever since.     A. is        B. was       C. has been        D. had been   答案：C已知函数f（x）=1x-1，0＜x＜11-1x，x＞1．（Ⅰ）当0＜a＜b，且f（a）=f（b）时，求1a+1b的值；（Ⅱ）若存在实数a，b（1＜a＜b），使得x∈[a，b]时，f（x）的取值范围是[ma，mb]（m≠0），求实数m的取值范围．