题目

In many countries around the world, parents give their babies ______ names so that they are different from others. A. formal    B. normal    C. common     D. unusual   答案：D考查形容词辨析. Formal正式的 ; normal 正常的 ; common 普通的,常见的 ; unusual 非同寻常的.已知a2+b2=4，b2+c2=3，c2+a2=3（a，b，c∈R），则ab+bc+ca的最小值为（ ）A．-5B．-2C．D．