Listen! There must be someone ______ at the door.

— Whose shirt is this?
— It ______ be Tony's. It is much too small for him.

— What do you think of this exhibition?
— Great.It's ______ exhibition I' ve ever seen.

Fast food ______ is not always bad for our health, but too much of ______ is not good.

— You remind me ______ Mr. Li. You wear the same jacket.
— Oh, it belongs ______ Mr.Li. He lent it to me.

— I can't learn English. I read my books but I always forget.
— Why not consider ______ flashcards?

Sam is ______ honest boy. If he makes ______ mistake, he will tell his parents.

（2011云南曲靖）如图：直线y=kx＋3与x轴、y轴分别交于A、B两点，tan∠OAB=,点C(x,y)是直线y=kx+3上与A、B不重合的动点.（1）求直线y=kx+3的解析式；（2）当点C运动到什么位置时△AOC的面积是6；（3）过点C的另一直线CD与y轴相交于D点，是否存在点C使△BCD与△AOB全等？若存在，请求出点C的坐标；若不存在，请说明理由.

(2010年浙江绍兴市)（1）如图1,在正方形ABCD中,点E,F分别在边BC,CD上,AE,BF交于点O,∠AOF＝90°.求证：BE＝CF.（2）如图2,在正方形ABCD中,点E,H,F,G分别在边AB,BC,CD,DA上,EF,GH交于点O,∠FOH＝90°,EF＝4.求GH的长.（3）已知点E,H,F,G分别在矩形ABCD的边AB,BC,CD,DA上，EF,GH交于点O,∠FOH＝90°,EF＝4.直接写出下列两题的答案：①如图3,矩形ABCD由2个全等的正方形组成,求GH的长；②如图4,矩形ABCD由n个全等的正方形组成,求GH的长(用n的代数式表示).

（2011贵州黔南）三角形两边长分别为3和6，第三边是方程的解，则这个三角形的周长是(            )