18．As any homemaker who has tried to keep order at the dinner table knows，there is far more to a family meal than food．Sociologist （社会心理学家）Michael Lewis has been studying 50families to find out just how much more．
Lewis and his co-workers carried out their study by videotaping（录像） the families while they ate ordinary meals in their own homes．They found that parents with small families talk actively with each other and their children．But as the number of children gets larger，conversation gives way to the parents'efforts to control the loud noise they make．That can have an important effect on the children．"In general the more question-asking the parents do，the higher the children's IQ scores．"
Lewis says，"And the more children there are，the less question-asking there is．"
The study also provides an explanation for why middle children often seem to have a harder time in life than their siblings（兄弟姐妹）．Lewis found that in families with three or four children，dinner conversation is likely to center on the oldest child，who has the most to talk about，and the youngest，who needs the most attention．"Middle children are invisible（看不见的），"says Lewis．"When you see someone get up from the table and walk around during dinner，chances are it's the middle child．"There is，however，one thing that stops all conversations and prevents anyone from having attention："When the TV is on，"Lewis says，"dinner is a non-event．"
56．The writer's purpose in writing the text is toD．
A．show the relationship between parents and children
B．teach parents ways to keep order at the dinner table
C．give information about family problems
D．report on the findings of a study
57．Parents with large families ask fewer questions at dinner becauseB．
A．they are busy serving food to their children
B．they are busy keeping order at the dinner table
C．they have to pay more attention to younger children
D．they are tired out having prepared food for the whole family
58．By saying"Middle children are invisible"in Paragraph 3，Lewis means that middle childrenA．
A．get the least attention from the family
B．have to help their parents to serve dinner
C．are often kept away from the dinner table
D．find it hard to keep up with other children
59．Lewis'research provides an answer to the questionD．
A．why TV is important in family life
B．why parents should keep good order
C．why children in small families seem to be quieter
D．why middle children seem to have more difficulties in life．
