What are standard & poor’s and moody’s? the largest issuers of junk bonds firms that rate bonds and publish the ratings financial intermediaries a part of the securities and exchange commission

Standard & Poor’s and Moody’s are  Firms that rate bonds and publish the ratings.
These companies would constantly research existing bonds and stocks in the market and analyze them. 
From the analyzation, they would separate the bonds and stocks into several grades based on their credibility in order to help potential investors to determine which one would be the best for them to buy.

Ithink it's a, but i might be wrong