—Why       your brother want      the tigers?
—Becausethey are very fun.

—Be quiet! Where is Clark?
—He      volleyball with his friends in the school gym.

Listen! Lily        the doll in the bedroom.

—       there any students in the classroom?
—No,there aren’t. But there       some half an hour ago.

—Allan, turn down the TV, please.I      on the phone.
—Oh,sorry.

—What does your brother like doing in his spare time?
—He        watching TV.

It’s eight o’clock. The students      an English class.

The teacher told us that the earth       around the sun.

已知：如图，A，B为直线l上两点，点为直线l上方一动点，连接，，分别以AC，BC为边向△ABC外作正方形CADF和正方形CBEG，过点D作DD₁⊥l于点D₁，过点E作EE₁⊥l于点E₁.
（1）如图1，当点E恰好在直线l上时(此时E₁与E重合)，试说明DD₁=AB；
（2）如图2，当D，E两点都在直线l的上方时，试探求三条线段DD₁，EE₁，AB之间的数量关系，并说明理由；
（3）如图3，当点E在直线l的下方时，请直接写出三条线段DD₁，EE₁，AB之间的数量关系.

已知：如图，在等腰直角三角形ABC中，∠ACB=90°，AC=BC=10cm，CD⊥AB于点D，如果点E在线段AC上以每秒2cm的速度由点C向点A运动，同时，点F在线段CB上以每秒1cm的速度由点C向点B运动．当点E停止运动时，点F也随之停止，设点E运动时间为t秒，若某一时刻△CED≌△BFD，求此时t的值．