如果看到“平江起义”、“百团大战”、“抗美援朝”、“共和国元帅”的解说词，那么介绍的历史人物应是（   ）

某地有座古民居叫千柱屋，是清代大地主斯元儒建造的私宅，建筑宏敞，因屋有千柱而得名。新中国建立以后，因一历史事件，几十户非斯元儒的后裔家庭住进了这座大宅。这一历史事件应该是（    ）

    This is a story about a famous American woman. Her name is Helen Keller. When she was only nineteen months old, she got an illness. It made her blind(瞎的) and deaf (聋的). She couldn't see or hear anything, so she couldn't learn to speak. When she was six, a young teacher came and taught her to read and write. Her name was Ann Sullivan.

    Later, when she was ten, Miss Sullivan took her to another teacher, Sarah Fuller. Sarah Fuller taught her to speak. Helen put her fingers on Miss Fuller's face and into her mouth. In this way, she learned to speak. She went to school and became famous because she was one of the first blind and deaf persons to learn to speak. She began to write books and to help the blind in many parts of the world. Her hard work and her courage(勇气) made people in all countries love her.

根据短文内容回答问题。

 是圆的两条弦，  是圆的一条直径且 平分 ，下列结论中不一定正确的是（   ）