Which of the following best completes the passage below People buy prestige when they buy a premium product. They want to be associated with something special. Mass-marketing techniques and price-reduction strategies should not be used because （）.

A．affluent purchasers currently represent a shrinking portion of the population of all purchasers

B．continued sales depend directly on the maintenance of an aura of exclusivity

C．purchasers of premium products are concerned with the quality as well as with the price of the products

D．expansion of the market niche to include a broader spectrum of consumers will increase profits

E．manufacturing a premium brand is not necessarily more costly than manufacturing a standard brand of the same product

测量附着水平，正确距离是（）

A.龈缘至袋底

B.牙颈部至袋底

C.龈缘至釉牙骨质界

D.釉牙骨质界至袋底

E.以上全不是