请阅读下列短文，从每题所给的四个选项(A、B、C和D)中，选出最佳选项。
E
The traditional distinction between products that satisfy needs and those satisfy wants is no longer adequate to describe classes of products. In today's prosperous societies, the distinction has become unclear because so many wants have been turned into needs. A writer, for instance，can work with paper and pencils. These are legal needs for the task. But the work can be done more quickly and efficiently with a word processor. Thus a computer is soon viewed as a need rather than a want.
In the field of marketing, consumer goods are classed according to the way in which they are purchased. The two main classes are convenience goods and shopping goods. Two lesser types are specialty goods and unsought(主动提供的)goods. It must be emphasized that all of these types are based on the way shoppers think about products. not on the nature of the products themselves. What is regarded as a convenience item in France (wine, for example) should be a specialty goods in the United States.
People do not spend a great deal of time shopping for such convenience items as groceries, newspapers, toothpaste, aspirin, and candy. The buying of convenience goods may be done routinely, as some families buy groceries once a week. Such regularly purchased items are called staples. Sometimes convenience products are bought without enough thinking; someone has a sudden desire for an ice cream sundae on a hot day. Or they may be purchased as emergency items.
Shopping goods are items for which customers search. They compare prices. quality, and styles, and may visit a number of stores before making a decision. Buying an automobile is often done this way.
Shopping goods fail into two classes: those that are recognized as basically the same and those that are regarded as different. Items that are looked upon as basically the same include such things as home appliances, television sets, and automobiles. Having decided on the model desired, the customer is primarily interested in getting the item at the most favorable price. Items regarded as essentially different include clothing, furniture, and dishes. Quality, style and fashion will either take precedence(优先)over price, or they win not matter at all.
子积为Kw，该温度下将a mol/L 一元酸 HA 与b mol/L一元碱BOH 等体积混合，若混合后溶液呈中性，下列说法一定正确的是（ ）
