题目

 Leonardo da Vinci___________ birds kept in cages in order to have the pleasure of setting them free.    A. is said to be buying            B. is said to have bought    C. is said to buy                 D. has said to have bought 答案：B13．下列说法正确的是（　　）A．10%的食盐溶液是指100g水中溶解了10g食盐B．某物质只含有一种元素，则该物质不可能是混合物C．世界是由物质组成的，物质都是由分子和原子构成D．生铁和钢是含碳量不同的铁的两种合金