**Core Concept**
The free edge of the lesser omentum is a peritoneal fold that contains the portal triad, consisting of the portal vein, hepatic artery proper, and hepatic ducts. During surgical procedures, such as cholecystectomy, the free edge of the lesser omentum is often divided to expose the gallbladder and bile ducts.

**Why the Correct Answer is Right**
When the free edge of the lesser omentum is reset or divided, the structures at risk of injury are the portal vein, hepatic artery proper, and common hepatic duct. The portal vein is the largest vein in the portal triad and is responsible for carrying venous blood from the gastrointestinal tract to the liver. The hepatic artery proper is a branch of the celiac trunk that supplies oxygenated blood to the liver. The common hepatic duct is formed by the confluence of the right and left hepatic ducts and drains bile from the liver into the common bile duct. The hepatic ducts are closely associated with the portal vein and hepatic artery proper, making them susceptible to injury during surgical dissection.

**Why Each Wrong Option is Incorrect**
* **Option A:** The portal vein is indeed at risk of injury during division of the free edge of the lesser omentum. However, it is not the only structure at risk.
* **Option B:** The hepatic artery proper is also at risk of injury, but the question asks for structures injured while resetting the free edge of the lesser omentum, which is more closely associated with the portal triad.
* **Option D:** The cystic duct is not directly associated with the free edge of the lesser omentum and is therefore not at risk of injury during this procedure.
* **Option E:** The common bile duct is formed by the confluence of the common hepatic duct and cystic duct and is not directly associated with the free edge of the lesser omentum.

**Clinical Pearl / High-Yield Fact**
Intraoperative injury to the portal triad can lead to significant morbidity, including bleeding, liver dysfunction, and biliary fistulae. Surgeons must take great care to identify and preserve the portal triad during surgical procedures involving the lesser omentum.

**Correct Answer: C**