下列条件能判定一个四边形是平行四边形的是（ ）
A．一组对边平行，另一组对边相等
B．一组对边平行，一组对角互补
C．一组对边平行，一组对角相等
D．两条对角线互相垂直
根据平行四边形的判定方法，只有C正确．
A、错误，等腰梯形满足此条件，但不是平行四边形．
B、错误，等腰梯形满足此条件，但不是平行四边形．
C、正确，可利用两直线平行，同旁内角互补，得出另一组对角也相等，从而判定是平行四边形．
D、错误，当这两条对角线的交点不是这两条对角线的中点时就不是平行四边形．
故选C．
| 完形填空。 | |||
| Nur Memet,a 53-year-old farmer,left his home in Shule County of Xinjiang early Saturday morning. With seven young trees on his bicycle,he joined a one-kilome-ter line of people 1 trees in his village. 2 the days when his grandpa's grandpa was alive,his family has been planting trees every spring. He has continued this tradition(传统) 3 over 30 years. His family is not 4 only one in Shule County with a tree-planting tradition, Shule County,which is near the Taklimakan Desert,gets 5 rainfall(降雨) per year. Each spring when the wind blows, Shule County has has "dust fall" 6 rainfall,with dust floating in the air. In order to fight the wind, the people 7 there have a long history of planting trees. They plant as many trees as they 8 for at least four or five days every March. Nur's house is now 9 by more than 400 trees.Though the road to the house is only three-meter 10 ,trees along the sides of the road are as tall as 20 meters. "When I was even shorter than a sheep,my mother told me again and again we should plant trees every year, " Nur said. | |||
| ( )1. A. planting ( )2. A. Because ( )3. A. for ( )4. A. a ( )5. A. many ( )6. A. next to ( )7. A. visiting ( )8. A. can ( )9. A. damaged ( )10. A. tall | B. cutting B. So B. in B. an B. few B. because of B. living B. must B. surrounded B. high | C. buying C. Since C.during C. / C. little C. nothing but C. moving C. may C. filled C. wide | D. selling D. However D. on D. the D. much D. instead of D. traveling D. need D. broken D. deep |