[单项选择]Question 10 is based on the following table.
RESULTS OF A CONTROLLED STUDY OF THE EFFECTS OF CHEWING GUM ON TOOTH DECAY IN CHILDREN
Average total number of new cavities per child over the course of three years
Children who regularly chewed gum sweetened with X 4.0
Children who regularly chewed gum sweetened with Y 1.5
Children who did not chew gum 2.5
Which of the following, if true, most helps to explain the difference among the children who chewed gum sweetened with X, the children who chewed gum sweetened with Y, and the children who did not chew any gum
A. X, but not Y, consists of a substance that helps to protect teeth against harmful substances present in other foods.
B. The children who did not chew any gum during the study ate fewer sweet foods than did either the children who chewed gum sweetened with X or the children who chewed gum sweetened with Y.
C. The action of chewing gum stimulates the production of saliva, which contains a substance that helps fight tooth decay, but X, unlike Y, is a contributing factor to tooth decay.
D. Each group of children who chewed gum during the study brushed their teeth more often than did the children who did not chew gum during the study, but the children who chewed gum sweetened with Y brushed their teeth less often than did the children who chewed gum sweetened with X.
E. (E) The action of chewing gum improves the circulation of blood in the jaw and strengthens the roots of adult teeth, but is also causes baby teeth to fall out more quickly than they would otherwise.