单项选择题

Unemployment (失业) rose from 7.5% in June, 1996 to 7.8% in July, 1996, the highest rate since January of that year , the Labor Department reported. The main mason was a large increase—nearly 700,000 in the labor force (劳动力), with a record 61.9% of the population over sixteen years of age working or actively looking for work. That growth was caused mainly by an increase in the number, of women in the labor force, an increase partly because of a continuation (持续) of long-term and economic trends (经济趋势) and partly a reflection (反映) of pressure (压力) on families to increase their incomes.
Which of the following is said to be the main reason why more people are looking for work