At the beginning of the 20th century, few people owned their homes (only around 19% of working families) or cars (at about ＄ 1,000 per ear this was well above the average family income of ＄ 650 per year), as most people were unable to borrow money. But there was a rapid rise in both home and car ownership during the mid-1900s.
Free time increased considerably following the shortening of the working week, i.e. from six days to five, and from 10 hours to eight hours a day. In fact, the working clay couldn't be too long, otherwise people wouldn't have the time to spend their money. The amount of a family's budget spent on outside entertainment, such as parties, films and concerts has increased from just under 6% in Ford's day to about 9% today. On the other hand, we spend only a quarter of what our great-grand-parents paid for reading materials.
It is difficult to see how our spending patterns may change in the future. We already know that our population is aging and this will have an effect on the amount of money we spend on medicalcare.
What is the subject discussed in the text？

A. Increase in family income.
B. Changes in family planning.
Changing patterns in spending.
Decrease in food demand.