连接OH，求证：∠DHO=∠DCO．

     My friend Tony is an American1 . He is ten years old. He lives 2  his family in China now. There are 3  people in his family; his mother Mrs Green, his father Mr. Green and his little sister Amy. He has a white cat. 4  name is Betty. Look ! Amy is playing 5  Betty. His father, Mr. Green,is watc­hing TV. His mother is doing housework. What about Tony? He is doing6 Chinese homework. He can't 7   Chinese well, but he likes Chinese very much.
    Tony's 8 works in a TV station. His father works in a school as an9 teacher. Tony and his sister10 to the same school.

设{b_n}是等差数列，b₁+b₂+b₃=15，b₃+b₅+b₇=33，S_n是数列{b_n}前n项和，令$T_n=\frac{4S_n+7}{b_n}$若$T_n\ge a$对一切的正整数n恒成立，则a的取值范围为（　　）

阅读材料，完成下列要求

近日，大型历史古装电视剧《芈月传》登陆北京卫视，不仅仅是这个“芈”（mǐ）字夺人眼球，该剧中大量的生僻字更是引发网友热议。对待生僻字，人们看法不一。有人认为：生僻字可以在一定程度上提升当代人的历史文化素养，因为在生僻字中往往蕴含着历史文化信息，或是有着时代的印记，可以勾起人们的历史记忆。也有人认为，语言的意义在于运用，文字用于交际的最终目的是追求简捷和效率，而生僻字影响了文字交际的使用价值。这些不常用的汉字已经没有意义了。