I think the best place to go on Sunday is the zoo. When you are 1, you can go there with your family.  2 the zoo, there are many animals: elephants, deer , 3, rabbits and other animals. Elephants are the 4 animals on land. I 5 there is a baby elephant in our zoo. So I want to 6 at it. Yu Xuan wants to go with me. She says, " 7 we go there together?" "Sure!" I say. "We can 8 a good time there. But let's 9 there at half past four. I have 10 homework to do."

已知双曲线$\frac{x^2}{a^2}-\frac{y^2}{b^2}=1\left(a>0,b>0\right)$的两焦点为F₁,F₂，过F₂作x轴的垂线交双曲线于A,B两点，若$△AB{F}_1$内切圆的半径为a，则此双曲线的离心率为（  ）

等腰直角三角形ABA₁的斜边为直角边向外作第3个等腰直角三角形A₁BB₁，…，如此作

下去，若OA=OB=1，则第n个等腰直角三角形的斜边长为____．