题目内容
In fig 1，ABCD is a quadrilsteral，E is a point the diagonal BD，EF∥AD，EM∥BC，then the value of | EF |
| DA |
| EM |
| BC |
（英汉词典：fig figure的缩写，图；quadrilateral四边形；diagonal对角线；value数值；variable变量；to depend on取决于；position位置）
四边形ABCD中，E是对角线BD上一点，EF∥AD，EM∥BC，则
| EF |
| DA |
| EM |
| BC |
| A、greater than 1（大于1） |
| B、equal to 1（等于1） |
| C、less than 1（小于1） |
| D、variable depending on the position of E（不能确定，与E的位置有关） |
分析：可由平行线的性质得出
=
，
=
，进而通过线段的转化即可得出结论．
| EM |
| BC |
| DE |
| DB |
| EF |
| AD |
| BE |
| BD |
解答：解：∵EM∥BC，
∴
=
，
∵EF∥AD，
∴
=
，
∴
+
=
+
=
=1．
故选B．
∴
| EM |
| BC |
| DE |
| DB |
∵EF∥AD，
∴
| EF |
| AD |
| BE |
| BD |
∴
| EM |
| BC |
| EF |
| AD |
| DE |
| BD |
| BE |
| BD |
| BE+ED |
| BD |
故选B．
点评：本题主要考查了平行线分线段成比例的性质问题，应能够熟练掌握．
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