Generate a question that has the following answer:  Speed begins to suspect that Racer X is actually his brother Rex in disguise  for the following movie plot:  Speed Racer (Emile Hirsch) is an 18-year-old whose life and love has always been racing. As a young boy, Speed shirked his schoolwork, only dreaming of being able to race one day as well as his older brother, Rex Racer (Scott Porter).However, Rex eventually had an altercation with his father Pops Racer (John Goodman), and never returned home. In the 2-3 years of racing that Rex did, viewers were divided, calling him both brave and a coward. However, it was during the final leg of the Casa Cristo road rally that Rex died in a fiery crash in the Maltese Ice Caves. After this event, Speed continued racing, with his lost Brother constantly on his mind.Now the prime driver for Racer Motors, Speed Racer is quickly sweeping the racing world with his skill, driving the "Mach 6" of his father's design, but remains interested only in the art of the race and the well-being of his family. Speed father is still adamant that Racer Motors continue to be an independent in a sport where almost everyone is owned by a large corporation.Shortly after Speed's most recent win, Mr. Royalton (Roger Allam), owner of conglomerate Royalton Industries, shows up at the family's doorstep. Inviting the Racer family to tour his company, Speed is somewhat impressed, yet a little apprehensive. Royalton gives Speed a week to consider his offer.Speed eventually returns to Royalton, and declines his offer, citing that racing is more of a family affair for him. Royalton then shows his true colors, revealing that top corporate interests(including himself) have been fixing races and cheating to gain profits for years. In retaliation for his refusal, Royalton promises that Speed will lose his next race that takes place in Fiji, and that Racer Motors will come under scrutiny as well (proof of the power that he holds, all his threats come to pass, leading to Speed's loss and the destruction of the Mach 6 racer).Shortly afterwards, the Racer family is visited by Inspector Detector (Benno Fürmann) and the mysterious Racer X (Matthew Fox). Both men are...

Who does speed suspect racer x is?