公平交易的原则有哪些（我记得有4个）——

fair trade
看罪恶都市"sin city"有句话就是"young girl lives,old man dies,fair trade"

解题思路：首先求出秤杆和秤盘的重心所在位置，即重心C到O点的距离，此时秤砣放在A点，根据杠杆平衡条件求OC的大小；然后求出在正常情况下（用1kg秤砣称3kg物品），秤砣到O点的距离L；
最后根据杠杆的平衡条件求出使用不标准的秤砣时（秤砣到O点的距离不变），消费者得到的物品实际质量．

设秤杆和秤盘的重心为C，当杠杆平衡时秤砣放在A点，∵G秤×OC=G砣×OA，即：m秤g×OC=m砣g×OA，0.5kg×OC=1kg×3cm，∴OC=6cm，使用1kg秤砣（正常情况下），设秤砣到O点的距离L，∵m物g×OB+m秤g×OC=m砣g×L 即：3...

点评：
本题考点： 杠杆的平衡分析法及其应用；杠杆的平衡条件．

考点点评： 本题考查了学生对杠杆平衡条件的掌握和运用，求出秤杆和秤盘的重心位置是本题的突破口，知道换了秤砣，秤砣到O点的距离不变，利用杠杆平衡条件求物品实际质量是本题的关键．

D

依法求偿权关键是求偿,本题中只是说不退还之类的,并没有涉及到索赔补偿,所以D不行.
一旦售出不能退换,也没有说他侵犯到交易的公平,也可以默认售出时时公平的交易.所以B不行
C就不解释了,直接排除.
自主选择权是指消费者可以根据自己的消费需求,自主选择自己满意的商品或服务,决定是否购买或接受的权利.消费者退换之类的,就是选择自己满意的商品,决定是否购买.所以是A.

D

Fair Value (Fair market Value) is also called Fair price,Fair.Familiar with the market situation of buyers and sellers in fair trading conditions and voluntarily under the situation of the price,or no correlation between the trade fair in under the condition of an asset can be sold or a liability can be off the price.It is in our use of overall experience from scratch,first withdrawal,and after advocating careful use and regulation of the process.The main consideration China as emerging market economies,many assets have not form the active market and the active market and open markets offer the best evidence that the fair value.On February 15,2006,China's ministry of finance promulgated new accounting standards for enterprises - basic standards,specific will fair value measurement attribute of the accounting,and accounting standards for specific in 17 different degree of using this measurement attributes.So as to change after the reform of fair value measurement attribute with previous old standards have what different,in handling and what need study place,put forward the new system after a series of problems in the application,and how to solve these problems,and how to better adapt to the new standard,this paper explores and studies the key content.