Many companies issue large number of stock options to executives and other employees (i.e., ESOs). These companies frequently buy back some of their shares on the open market. For example, Microsoft Corp., which was a major issuer of ESOs, bought back over $20 billion of its shares over a five-year period up to 2003. In February 2005, ConocoPhillips, a large U.S. oil company based in Houston, Texas, announced a $1 billion buyback program over the next two years. ConocoPhillips was also a major ESO issuer. (a) Why would firms with large ESO plans buy back their own stock? Explain