Which of the Following Demographic Shifts Is Having the Biggest

Which of the following demographic shifts is having the biggest impact on the traditional "three-stage model of work life?"

A) People who have retired from one career taking up part-time employment in another line of work.
B) Young people working part-time while attending school.
C) Immigrants saving money to sponsor family members to follow them to Canada.
D) Women returning to the paid labour force after their children start school.