如图，在梯形<span>ABCD</span>中，<span>AB=2</span>，<span>CD=3</span>，<span>AC</span>交<span>BD</span>于<span>O</span>点，过<span>O</span>作<span>AB</span>的平行线交<span>BC</span>于<span>E</span>点，连结<span>DE</span>交<span>AC</span>于<span>F</span>点，过<span>F</span>作<span>AB</span>的平行线交<span>BC</span>于<span>G</span>点，连结<span>DG</span>交<span>AC</span>于<span>M</span>点，过<span>M</span>作<span>AB</span>的平行线交<span>BC</span>于<span>N</span>点，则线段<span>MN</span>的长为（<span> </span>）<span></span> <img src="http://www.sdsgwy.com/tiku/img/yunsuan/0lah46wni.png" alt="" />