A conventional mortgage purchased by FNMA requires all of the following except

* A strong FICO score of at least 620 but closer to 730 to get the lowest rates * Monthly homeowners expenses won't exceed 28 percent of your gross monthly income; exceed more than 36 percent of your gross monthly income * A down payment of 20% ( or mortgage insurance) * Mortgage term must be 30 years * All of the four are required

please explain why