The Yankees experienced an eventful April, filled with highs and lows. Fortunately, the good times significantly outweighed the bad ones , painting a bright outlook as the calendar turns to May. Now, all eyes will be on the Yankees to see if their strong start was a mirage or if this team is truly built to challenge for a World Series. Even in the best championship contenders, no situation is ever perfect. There's always room for improvement. Yankees general manager Brian Cashman can use the trade market to find lineup upgrades , sure, but he and manager Aaron Boone can also use internal options to solve their problems. New York has a handful of up-and-coming arms and bats who are almost ready to make a big league impact. Here are three prospects the Yankees could promote to the majors before May ends, starting with the most obvious candidate. 1. George Lombard Jr., IF George Lombard Jr. continues to ascend through the Yankees' system. How long until he makes his MLB debut?…