31. Describe the business purpose, step-transaction, and substance-pver-form doctrines. What types of tax planning strategies may these doctrines inhibit? 32. What is the difference between tax avoidance and tax evasion? 38. Isabel, a calendar-year taxpayer, uses the cash method of accounting for her sole proprietorship. In late December she received a $20,000 bill from her accountant for consulting services related to her small business. Isabel can pay the $20,000 bill anytime before January year, and that she can earn an after-tax rate of return of 12 percent on her investments. When should she pay the $20,000 bill - this year or next