B、the difference between national income and personal income
C、the concept of income
D、the difference between disposable income and nondisposable income
16. Paragraph?17. Paragraph?18. Paragraph?19. Paragraph?20. Paragraph?A. What is the function of audio courses?B. What is the function of flash cards?C. What is the function of traditional courses?D. What are the most useful tools for language learning?E. What is the function of computeraided courses?F. What can help you a lot with your language learning?