根据下列材料请回答 31～35 题：
Stop Eating Too Much
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 too many bites． Instead of staying“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 tyro give them that． They prefer to have customers complain about too much food rather than too little．
Barbara Rolls，a nutrition(营养)professor at Pennsylvania State University, told USA- faddy that restaurant portion sizes began to grow in the 1 970s，the same time that the American waistline(腰围)began to expand．
Health experts have tried to get many restaurants to serve smaller portions.Now， apparently, some customers are calling for this too．The restaurant industry trade magazine QSR reported last month that 57 percent of more than 4，000 people surveyed believed restaurants served portions that were 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 earn 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(薪金支票)to paycheck，happy to save a little money for next year’s Christmas presents．
第 31 题 Parents in the United States tend to ask their children

A. to save food for tomorrow.
B. to wash the dishes.
C. mottos eat too much.
D. not to waste food.