Complex sentence: To become colorectal surgeons, these surgical doctors have to complete a general surgery residency, as well as a colorectal surgery fellowship, upon which they are eligible to be certified in their field of expertise by the American Board of Colon and Rectal Surgery.
Split into simpler sentences: To become colorectal surgeons, these surgical doctors have to complete a general surgery residency, as well as a colorectal surgery fellowship, upon which they are eligible to be certified in their field of expertise. In the United States, some surgeons (MDs) are certified by the American Board of Colon and Rectal Surgery.