**Core Concept**
Liver enlargement after transplantation is a common phenomenon due to the presence of various factors. The liver undergoes a process called "reinnervation" after transplantation, where the nerve endings from the new liver start to grow and stimulate the liver cells to increase in size.

**Why the Correct Answer is Right**
The liver enlargement after transplantation is mainly due to the increase in the size of the hepatocytes. This is caused by the reinnervation of the liver, which leads to an increase in the expression of growth factors and hormones that stimulate the liver cells to proliferate. The reinnervation process is thought to be mediated by the growth of nerve fibers from the vagus nerve, which innervates the liver and regulates its function.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because liver enlargement after transplantation is not primarily due to the accumulation of ascites or edema, which are conditions that can cause liver enlargement in other contexts.

**Option B:** This option is incorrect because liver transplantation itself does not cause liver enlargement due to the presence of a liver mass or tumor.

**Option C:** This option is incorrect because liver enlargement after transplantation is not primarily due to the presence of a liver abscess or other infectious process.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that liver enlargement after transplantation can be a normal finding and is often seen in the early stages after surgery. However, large liver enlargement can be a sign of complications such as reperfusion injury or rejection.

**Correct Answer: C. Rejection.