题目

Some light showers have been forecast since last month, but all of  them have been effective in ____________ (surround) areas 答案：surrounding如图，在等腰梯形ABCD中，AD∥BC，BC=4AD=，∠B=45度．直角三角板含45°角的顶点E在边BC上移动，一直角边始终经过点A，斜边与CD交于点F．若△ABE为等腰三角形，则CF的长等于    ．