You're a slightly cocky bond portfolio manager and you're trying to do better than the returns on a buy-and-hold strategy.You've decided to try using credit analysis to find bonds whose current bond rating is too low.You will then increase the weight of those bonds in your portfolio.You found one right away.XYZ Inc.'s bonds were rated BB in April and your analysis indicated they were better (less risky) than that.You put 20% of the portfolio into XYZ bonds and you were elated to open the Wall Street Journal this morning and see that the rating agency had indeed upgraded those bonds to BBB+.When you bounced into work, you saw to your amazement that there had been no change in the price or the return on XYZ's bonds (and normal daily volume of a few hundred bonds traded).Why did your strategy fail to pay an excess return?Show all work.