题目

完形填空Animals are our friends.We can find different__1__of animals.Some animals are living __2__ big woods(森林)．And some animals are living with __3__.Why？Because they can __4__ for us.People can teach the elephant to do some heavy __5__.And they can also teach the dog to __6__the house.A watch dog is very _7__.It can help people in danger(处于危险中)．Children__8__dogs very much.__9__of children like to go to the zoo.__10__ there are many animals in the zoo.A zoo is a good place for children to get to know animals.1．A.kind            B．a kinds        �如图，A1A是圆柱的母线，AB是圆柱底面圆的直径，C是底面圆周上异于A、B的任=A意一点，A1A=AB=2．（1）求证：BC⊥平面A1AC；（2）求三棱锥A1-ABC的体积的最大值．