下列关于x的一元二次方程中，有两个不相等的实数根的方程是（ ）
A．x2+1=0
B．x2+x-1=0
C．2x2+2x+3=0
D．4x2-4x+1=0
A、x2+1=0中△＜0，没有实数根；
B、x22x-1=0中△＞0，有两个不相等的实数根；
C、2x2+2x+3=0中△＜0，没有实数根；
D、4x2-4x+1=0中△=0，有两个相等的实数根．
故选B．
| 完形填空。 | |||
| Thomas Edison was a famous American scientist. He was ____1____ in 1847. When he was a child, he liked to ____2____ out how things worked. He was in school ____3____ only three months. He asked his teacher a lot of strange questions. Most of them had nothing ____4____ his lessons. The teacher thought the boy was not bright. So Edison’s mothertook her son ____5____ of school. As she had been a teacher, she taught his ____6____. The boy read a ____7____. Soon he became very____8____ in science. At the age of ten, Edison had already ____9____ a chemistry lab for himself. When he grew into a young man, he __ 10 many important things for man. All these things have changed the whole world. Can you name some of his inventions? | |||
| ( )1. A. taken ( )2. A. look ( )3. A. for ( )4. A. about ( )5. A. into ( )6. A. myself ( )7. A. lot ( )8. A. glad ( )9. A. built ( )10.A. taken | B. born B. speak B. in B. on B. at B. yourself B. little B. angry B. made B. invented | C. killed C. find C. at C. with C. front C. herself C. few C. excited C. produced C. made | D. caught D. watch D. on D. in D. out D. himself D. many D. interested D. grown D. planted |
型的特点为（）。