题目

Donald Duck was born on June 9, 1934. Now he is 71 years old． He is the oldest duck in the world．He is very funny. He makes a lot of people laugh again and again. Children around the world all like him. He first appears （出现）in the cartoon The Wise Little Hen. The little hen works very hard．But Donald Duck and his friend Peter Pig do not want to work. Then the little hen gives them a lesson. She tells them that work is important. Donald is like a little man in a big world．He has a good heart. He wants to help others. But things .always go wrong for him. He doesn't like it. He ge若方程ax2+bx+c=0（a≠0）满足a+b+c=0，则方程必有一根为（ ）A．0B．1C．-1D．±1