优势菌是伴放线放线杆菌的牙周疾病是（） A.健康牙周 B.龈炎 C.慢性成人牙周炎

若数列{a_n}的前n项和为S_n，则下列命题：

（1）若数列{a_n}是递增数列，则数列{S_n}也是递增数列；

（2）数列{S_n}是递增数列的充要条件是数列{a_n}的各项均为正数；

（3）若{a_n}是等差数列（公差d≠0），则S₁•S₂…S_k=0的充要条件是a₁•a₂…a_k=0．

（4）若{a_n}是等比数列，则S₁•S₂…S_k=0（k≥2，k∈N）的充要条件是a_n+a_n+1=0．

其中，正确命题的个数是（　　）

A．0个

B．1个

C．2个

D．3个

短文改错（共10小题；每小题1分，满分10分）

1. 请按标准格式改错，每处错误及其修改均限一词。

2. 只允许修改10处，多者（从第11处起）不计分。

Though great progress has made in science these years, there

are still many people lived in poor conditions. They make their living

by collecting and selling used thing. Their children cannot go to school

because they have no enough money to send their children to there.

Why you think so many people still suffer from poverty now?

The answer lies on the population explosion. A president of a developing

country once said: “It is us who are to blame for the poverty because we used to

produce child without limit.” Although these few words sound simple enough,

but they have clear pointed out one of the causes of the population explosion.

某车间要制造a个零件，原计划每天制造x个，需要______天才能完成；若每天多制造b个，则可提前______天完成．

神仙一块气功效与作用

下列地点在近代中国被迫开放为通商口岸的先后顺序是( )。
①天津 ②福州 ③南京 ④重庆

A．②③①④
B．①②③④
C．②①④③
D．③④①②