什么叫菌种退化？如何区别衰退、饰变与杂菌污染？

If you go into the forest with friends, stay with them .If you don’t, you may get lost. If you do get lost, this is what you should do. Sit down and stay where you are. Don’t try to find your friends. Let them find you. You can help them to find you by stay in one place.

There is another way to help your friends or other people to find you. Give them a signal(信号)outing or whistling (吹口哨) three times. Stop. Then shout or whistle three times again. Any signal given three times is a call for help.

Keep on shouting or whistling, always three times together. When people hear you, they will give two shouts or two whistles. When a signal is given twice, it is an answer to a call for help.

If you don’t think that you will get help before night comes, try to make a small room with branches.（树枝）

What should you do if you get hungry or need drinking water? You would have to leave your little branch room to look for something to eat and drink. Don’t just walk far away. Pick up small branches and drop them as you walk so that you can find your way back.

The most important thing you need to do when you are lost ---stay in one place.

小题1:When you hear two shouts or whistles, what does that mean?

A．Some animals are coming.

B．Someone is calling for help.

C．People will come to help you

D．Someone is lost.小题2:What shouldn’t you do, if you get lost in the forest?

A．Walk everywhere to find your friends.

B．Sit down and stay where you are.

C．Make a small room with branches.

D．Try to find something to eat and drink小题3:Which of the following is wrong according to the passage?

A．You can leave your branch room to find some food.

B．You can’t go anywhere even when you feel thirsty or hungry.

C．You should leave some branches as you walk.

D．Don’t go far away from your room.

将氢气、甲烷、乙醇等物质在氧气中燃烧时的化学能直接转化为电能的装置叫燃料电池．燃料电池的基本组成为电极、电解质、燃料和氧化剂．此种电池能量利用率可高达80%，产物污染也少．下列有关燃料电池的说法错误的是[ ]

A．上述燃料电池的负极反应材料是氢气、甲烷、乙醇等物质

B．氢氧燃料电池常用于航天飞行器，原因之一是该电池的产物为水，经过处理之后可供宇航员使用

C．乙醇燃料电池的电解质常用KOH，该电池的负极反应为：C₂H₅OH－12e^－===2CO₂↑＋3H₂O

D．甲烷燃料电池的正极反应可以为：O₂＋2H₂O＋4e^－===4OH^－

关于传播途径的描述，下列错误的是（）

A.传染途径既可是单一因素，也可是外界多种因素组成

B.手、玩具既可传播消化道传染病，也可传播呼吸道传染病

C.传播传染病的节肢动物是中间宿主

D.血液、血制品是乙型肝炎、丙型肝炎等的最主要传播途径

E.破伤风通过未经严格消毒的刀、剪传播，而污染土壤不会造成传播

测量某段距离，往测为120.456m，返测为120.485m，则相对误差为

A．1/4300

B．1/4200

C．0.0290

D．0.000241

乌梅丸中用来下蛔的药物是（）

A.乌梅

B.细辛

C.附子

D.干姜

E.黄连