题目

 It was said that Jack was already very famous as a dancer ____in the USA when he was only twelve.    A. in his twenties    B. on the twenties    C. of twenty      D. in the twenties 答案：D6．先化简，再求值：$（1+\frac{1}{x-2}）÷\frac{x-1}{{{x^2}-4x+4}}$，选择一个你喜欢的数代入求值．