自然条件下，生态系统具有抵抗力稳定性，是因为（） A.生态系统具有一定的自动调节能力

一公司有10个雇员，5个人的年薪为20000元，4个人的年薪是25000元，1个人的年薪是30000元。如果奖金数占他们年薪的10%，问该公司一年要发多少奖金

A．75000元
B．30000元
C．23000元
D．7500元

     If you have no special plans for your holidays, why not be a volunteer with us? Being a volunteer, you don’t think only of         . You work, and you don’t get money.         your helping hands can make both others and yourself happy. More and more young people are ready to           us. Let’s share some of their stories and plans.

Mary, 17

I visited the forest park with Mr Cao last week. I found there were not enough         there. I’m going to help the Forest Centre build new hiking paths in the mountains. It’s going to be great           —I’ll spend seven days living in a forest and enjoying the clean mountain air. I’m going to           with friends in the day and then sleep under the moon and stars. It will be a nice sport, and I’ll be able to do         good at the same time.

Andy, 18

This summer, I’m going to volunteer with Loving Pets Program. I         my neighbours’ pets last summer. And I fell in love with dogs and cats. This summer, I will work in the         centre and         my kindness and love to more pets. I am sure to make friends with more       !

Haitao, 16

Some children find reading         . They have problems with reading. They need our help. I’ll work for a       called Reading for Life. Every day, I’m going to help them choose and read books            they like. I want to be a          when I grow up, and I love children and reading, so this experience will help me in many ways.

在pH＝9的NaOH溶液和CH₃COONa溶液中，设由水电离出的OH^－浓度分别为M和N，则M和N的关系为 [ ]

A．M>N

B．M＝10^－4N

C．N＝10^－4M

D．M＝N

一条小街上顺次安装10盏路灯，为了节约用电又不影响路面照明，要关闭除首末两灯以外的8盏灯中的4盏灯，但被关的灯不能相邻，共有______不同的关法．

与辐射有关的肿瘤有（）

A.淋巴瘤

B.乳腺癌

C.甲状腺癌

D.白血病

E.皮肤癌