化简AB-CD-AC+BD=______．

根据短文内容和首字母提示，在下文空格处填入适当的词使短文完整。（每空一词）

Dear Peter,

I’m glad to receive your letter. Thank you for your caring a     the weather and my health. Now I’d like to tell you something about the smog（雾霾）.

Since the winter last year, the smog has taken place for several times. It has done great harm(伤害) to our d­     life. Many traffic accidents have happened because of the h     smoggy weather. More and more people have to go to see a d     because of the serious diseases(疾病) caused by the smog. Quite a lot of flights have to be put off. A great number of people have to s     at home for fear of the poisonous(有毒的) air caused by the smog.

People have realized(意识到) the great harm caused by the smog and the importance of

p     the environment. People from all over the country are taking a     to improve the smoggy weather. The government asks people to go to work or school with public traffic tools, such as the bus and the u    . Also we should plant more trees.

According to me, I will go to school by bike or on foot, and I won’t throw the waste anywhere. M     , I will tell people that all of us should protect the environment as p     as we can. Would you like to tell me some good ideas? I’m looking forward to your reply.

Yours,

Wang Hua

地球上各种不同类型的生态系统具有不同的调节能力。与农田、草原、冻原等生态系统相比较，热带雨林的自我调节能力特点是[ ]

A．种群数量调节能力强，抵抗外界干扰能力弱

B．分解力弱，生产力强

C．抵抗外界干扰能力强，自我恢复能力弱

D．能量流动速度快，物质循环速度慢

卖出看跌期权的风险和收益关系是( )。

A．损失有限，收益无限

B．损失有限，收益有限

C．损失无限，收益无限

D．损失无限，收益有限

下图是“我国东、中、西部部分指标占全国比重示意图”。读图回答21～22题。

小题1:图中反映出制约我国西部地区经济发展的因素是

①人才缺乏      ②交通落后      ③资源短缺      ④外商投资少

A．①②③

B．②③④

C．①②④

D．①③④小题2:下列措施中，对中西部地区吸引外资见效最快的是

A．加大铁路建设力度

B．加大政策支持力度

C．加大资源开发力度

D．加大人才培养力度

研究表明，随着年龄的增加，人的基础代谢率下降，能量消耗减少，体重和体脂会慢慢地增加。