请教CXD削弱T5

The ratio of divorce to marriage has increased since 1940. Therefore, there must be a greater proportion of children living with only one natural parent than there was in 1940.

Which of the following , if true , most strongly weakens the inference drawn above?

A.      The number of marriages entered into by women twenty-five to thirty-five years old has decreased since 1940.

B.      When there is a divorce, children are often given the option of deciding which parent they will live with.

C.    Since 1940 the average number of children in family has remained approximately steady and has not been subject to wide fluctuations.

D.    Before 1940 relatively few childfren whose parents had both died were adopted into a single-parent families.

E.     The proportion of children who must be raised by one parent because the other has died has decreased since 1940 as a result of medical advances.

Ans:E,这题花了2分38秒，读完题干，没有思路。不明白为何E对？另外，对付这种数字比例的题目，不知有什么办法？

谢谢