如图,在单位长度为1的正方形网格中建立一直角坐标系,一条圆弧经过网格点A、B、C,请在网格图中进行下列操作(以下结果保留根号)：

（1）利用网格确定该圆弧所在圆的圆心D点的位置,并写出D点的坐标为            ；
（2）连接AD、CD,则⊙D的半径为        ,∠ADC的度数为        ；
（3）若扇形DAC是一个圆锥的侧面展开图,求该圆锥底面半径．

阅读短文，判断正误。用“正确”或“错误”表示。

Penguins are good swimmers, and they are very good at swimming in the sea. They can dive much deeper than people. Some people can dive about 180 metres, but most people can only dive about 30 metres. Penguins can dive 500 metres. That is a long way down! Do you know the TV Tower in Shanghai? That is 468 metres high.

 Penguins can hold their breath much longer than people.Some people can hold their breath for about five minutes, but most people can only hold their breath for one or two minutes. Penguins can hold their breath for 20 minutes.

Many whales can hold their breath longer than penguins. Some whales can hold their breath for about two hours!

①它是社会主义初级阶段基本经济制度的重要实现形式

②它的发展有利于各种所有制资本相互促进，共同发展

③它的发展使国家在更多领域放弃国有经济的主体地位

④它能使各种所有制平等竞争从而增强经济的控制力

       《海底两万里》是凡尔纳的三部曲的第二部，另外两部分别是____和____。《海底两万里》主要讲述____的故事。小说中____是个不明国籍的神秘人物，他在荒岛上秘密建造的这艘潜艇。