在Visual FoxPro中，建立索引的作用之一是 ______。

A．节省存储空间

B．便于管理

C．提高查询速度

D．提高查询和更新的速度

"Clean your plate!" and "Be a member of the clean-plate club!" Just about every kid in the US has heard this from a parent or grandparent. Often, it’s accompanied by an appeal. "Just think about those starving orphans (孤儿) in Africa!"
Sure, we should be grateful for every bite of food. Unfortunately, many people in the US take a few too many bites. Instead of saying "clean the plate," perhaps we should save some food for tomorrow.
According to news reports, US restaurants are partly to blame for the growing bellies (肚子). A waiter puts a plate of food in front of each customer, with two to four times the amount recommended by the government, according to a USA Today story.
Americans traditionally associate quantity with value and most restaurants try to give them that. They serve large portions to stand apart from competitors and to give the customers value. They prefer to have customers complain about too much food rather than too little.
Barbara Rolls, a nutrition professor at Pennsylvania State University, told USA Today, that restaurant portion sizes began to grow in the 1970s, the same time that the American waistline began to expand.
Health experts have tried to get many restaurants to serve smaller portions. Now, apparently, some customers are calling for this too. A restaurant industry trade magazine reported last month that 57 percent of more than 4 000 people surveyed believed restaurants serve portions that are too large; 23 percent had no opinion; 20 percent disagreed.
But a closer look at the survey indicates that many Americans who can’t afford fine dining still prefer large portions. Seventy percent of those earning at least $150 000 per year prefer smaller portions, but only 45 percent of those earning less than $ 25 000 want smaller.
It’s not that working class Americans don’t want to eat healthy. It’s just that, after long hours at low-paying jobs, getting less on their plate hardly seems like a good deal. They live from paycheck to paycheck, happy to save a little money for next year’s Christmas presents.

According to news reports. US restaurants ______.

A. are partly responsible for the overweight problem
B. ignore the government regulations on food amount
C. serve two to four times the amount the customers want
D. are partly to blame for the waste of food in America