The combining form that means abdomen is celio.
Here’s a brief explanation: In medical terminology, specific prefixes, suffixes, and combining forms are used to describe various parts of the body. The combining form ‘celio’ is derived from the Greek word ‘koilia,’ which refers to the abdominal cavity. It is commonly used in words related to the abdomen, such as ‘celiopathy’ (a disease of the abdomen) and ‘celioscopy’ (a surgical procedure involving the abdomen).
In contrast, ‘cephalo’ refers to the head, ‘aorto’ relates to the aorta (the main artery in the body), and ‘cerebro’ pertains to the brain. Therefore, the correct answer is ‘celio.’