What does the word rapid in the first paragraph mean?

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.
Many years ago, people often said “A woman's place is in the home”. But Americans do not feel that way anymore. Today, women make up about 43 percent of the America labor force. There are about 45 million working women in the United States, and a large number of them are married women with children. In 1980, for the first time in the nation's history there were more working wives than household wives. Looking back to 1940, we can see picture of some very rapid change. In 1940, only 15 percent of married women held jobs.
Today, most young women choose to work even when they have young children. Why do they work? The most important reason is that they need to earn money. But another reason is that women today are better educated and they have more opportunities to work in various professions than women had earlier.