有下列反应：2KMnO4+5K2SO3+3H2SO4══6K2SO4+2MnSO4+3H2O，在反应中还原产物和氧化产物的物质的量之比为（ ）
A．1：4
B．1：3
C．2：5
D．3：2
在反应2KMnO4+5K2SO3+3H2SO4═6K2SO4+2MnSO4+3H2O中，锰元素化合价由+7价降低为+2价，锰元素被还原，还原产物是MnSO4，硫元素化合价由+4价升高为+6价，硫元素被氧化，氧化产物是K2SO4．由方程式可知，锰元素全部被还原，+4硫元素全部氧化，根据化学计量数判断氧化剂KMnO4与还原剂K2SO3的物质的量之比为2：5．由于KMnO4～MnSO4，K2SO3～K2SO4，所以反应中还原产物和氧化产物的物质的量之比为2：5．
故选C．
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| Everyone in business has been told that success is all about attracting and retaining (留住) customers. It sounds simple and achievable. But, 1 , words of wisdom are soon forgotten. Once companies have attracted customers they often 2 the second half of the story. In the excitement of beating off the competition, negotiating prices, securing orders, and delivering the product, managers tend to become carried away. They forget what they regard as the boring side of business- 3 that the customer remains a customer. 4 to concentrate on retaining as well as attracting customers costs business huge amounts of money annually. It has been estimated that the average company loses between 10 and 30 per cent of its customers every years. In constantly changing 5 , this is not surprising. What is surprising is the fact that few companies have any idea how many customers they have lost. Only now are organizations beginning to wake up to those lost opportunities and calculate the 6 implications. Cutting down the number of customers a company loses can make a big 7 in its performance. Research in the US found that a five per cent decrease in the number of defecting (流失的) customers led to 8 increases of between 25 and 85 per cent. In the US, Domino's Pizza estimates that a regular customer is worth more than $5,000 over ten years. A customer who receives a poor quality product or service on their first visit and 9 never returns, is losing the company thousands of dollars in 10 profits (more if you consider how many people they are likely to tell about their bad experience). The logic behind cultivating customer 11 is impossible to deny. "In practice most companies' marketing effort is focused on getting customers, with little attention paid to 12 them", says Adrian Payne of Cornfield University School of Management. "Research suggests that there is a close relationship between retaining customers and making profits." 13 customers tend to buy more, are predictable and usually cost less to service than new customers. Furthermore, they tend to be less price 14 , and may provide free word-of-mouth advertising. Retaining customers also makes it 15 for competitors to enter a market or increase their share of a market. | ||||
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