题目

He’d like some ________ and ________. A. beef, tomatoes    B. beefs, tomatoes    C. beef, tomato      D. beefs, tomato 答案：A1．化简：a${\;}^{\frac{2}{3}}$•a${\;}^{\frac{1}{5}}$•a${\;}^{\frac{7}{15}}$（a＞0）．