Yield curves may be used to illustrate the term structure of interest rates. A yield curve may be most accurately described as

1. a graph showing total returns on a sample of related securities.
2. the relationship between yield and term-to-maturity for securities that are uniform in terms of default risk.
3. the relationship between yield and term-to-maturity for government securities.
4. the relationship between yield and term-to-maturity for all debt securities in the market at a given time.