已知各项均为正的等比数列{bn}的首项b1=1，公比为q，前n项和为Sn，若li

请你根据下列粒子的结构示意图判断，选项中哪种物质是由所提供的粒子构成的（______）　

A、MgCl₂ B、KCl       C、k₂O     D MgO．

为保护朱鹩，在陕西省建立了_______保护区；为了保护斑头雁，棕头鸥等鸟类及其栖息环境，在青海省建立了_______自然保护区。

阅读下列短文，从每题所给的四个选项(A、B、C和D)中，选出最佳选项，并在答题卡上将该项涂黑。

C

Reading can be a social activity. Think of the people who belong to book groups. They choose books to read and then meet to discuss them. Now, the website BookCrossing.com turns the page on the traditional idea of a book group.

Members go on the site and register the books they own and would like to share. BookCrossing provides an identification number to stick inside the book. Then the person leaves it in a public place, hoping that the book will have an adventure, traveling far and wide with each new reader who finds it.

Bruce Pederson, the managing director of BookCrossing, says, “The two things that change your life are the people you meet and books you read. BookCrossing combines both.”

Members leave books on park benches and buses, in train stations and coffee shops. Whoever finds their book will go to the site and record where they found it.

People who find a book can also leave a journal entry describing what they thought of it. E-mails are then sent to the BookCrossing to keep them updated about where their books have been found. Bruce peterson says the idea is for people not to be selfish by keeping a book to gather dust on a shelf at home. zxx.k

BookCrossing is part of a trend among people who want to get back to the “real” and not the virtual(虚拟). The site now has more than one million members in more than one hundred thirty-five countries.

What is the best title for the text?（）

A. Online Reading: A Virtual Tour

B. Electronic Books: A new Trend

C. A Book Group Brings Tradition Back

D. A Website Links People through Books

按显示功能热工仪表分为那几类？

苛化回收Na₂O的方法是（），其反应式（）