T/F questions but please answer WHY they are either true or false. 1-2 sentences

1. Liquidity refers to how quickly you can sell a security
2. A shift in the demand for UST securities should cause yields to fall, all else equal.
3. At the peak of the business, you would expect default risk premiums to be at its widest.
4. The yield to maturity is a good estimate of your expected return for risky securities if you plan to hold the security to maturity.
5. Bond ratings are a good forward-looking measure of default risk.
6. The bid-asked spreads for corporate bonds are the same for all ratings categories
7. Default risk premiums are constant across maturity for a given security and rating
8. If the S&P 500 EP yield is below the 10-year UST, an argument can be made that the stock market is undervalued.