题目

先化简，再求值2(3a2b-ab2)-(ab2+2a2b)+3ab2,其中a= ,b=-6 答案：解：原式 =6a2b−2ab2−ab2−2a2b+3ab2 =4a2b将 a=12,b=−6 代入得：原式 =4×(12)2×(−6)=4×14×(−6)=−6 .听下面一段材料，回答第1至3三个小题。 1. What are the two speakers' nationalities? [     ]A. British and Chinese. B. Chinese and French. C. Chinese and American. 2. What problem was a newspaper article about? [     ]A. The problem of rapid growth of cars in cities in America. B. The problem of rapid growth of cities in America.C. The problem of rapid growth of skyscrapers. 3. Do Americans carry out a birth control policy? [     ]A. Yes, they do. B. No, they don't. C. We can't know. 4. What attitudes do most Americans take towards having children? [     ]A. Most Americans decide not to have any children. B. Most Americans decide to have as many children as they can. C. Most Americans decide to have only one or two children.