Questions 31 to 35 are based on the following passage.
Americans are a very energetic and mobile people, always on the run; rushing from one appointment to another, from a PTA (Parent Teacher Association) meeting to a social planning committee. They have very little time to spend preparing elaborate（精致的，复杂的）everyday meals to be eaten at leisure. In many homes it is rare for the whole family to sit down at supper together. Clubs and committees force them to grab a quick meal rather than a sit-down supper.
When they do have the chance to eat at home, often the working housewife prefers to prepare meals that can be quickly heated and consumed. It is no wonder, therefore, that America has become a shelter for fast food consumption.
This great transformation occurred after World War Ⅱ when many women began to work full time and spend less time at home with their families. Women, however, wanted to function well in the capacity of homemaker, as well as that of career woman but time became a precious commodity（商品）which had to be carefully used.
Therefore, it was necessary to make her life easier at home in the preparation of the family dinner. Simultaneously with women entering the job market there was also a shifting of the focus of home entertainment from the radio to the television. Television became the latest fashion in the 1950s and no one wanted to miss his or her favorite programs. And then, the place for supper shifted from the dining room to the living room.
As the customs changed, so did the culture. The immediate solution for this was the invention of the TV dinner. These were frozen meals which were divided into portions of meat and vegetables. They could easily be put into an oven（锅）and prepared within minutes. The tin trays（托盘）in which they were served were conveniently carried into the living room and dinner was consumed in front of a TV set. Cleaning up afterwards was no problem. The tin trays were easily thrown into the garbage.
From fast dinners at home the next step was quick eating while on the road. Love for TV was combined with the fascination for the automobile. It is not odd that with the development of the superhighways America saw the beginning of fast food chains. McDonald's paved the way with its variety of burgers and cold drinks soon to be followed by all kinds of other foods. Today dozens of fast-food chain stores can be found along highways, in modern shopping malls and scattered throughout neighborhoods in America. Taco Bell, Pizza Hut, Roy Roger's, Burger King and Wendy's are just a few of the fast-food chains which are now part of American culture． They offer chicken, donuts, tacos and pizza, all quickly produced in great quantities for the masses. These establishments have given shape to the modern lifestyles and diet of the American people.
31．In America, the whole family seldom have dinner together at home because＿．
A．they have so many social activities
B．they have a lot of meetings to attend
C．they rush from one appointment to another
D．they often move from one place to another