**Core Concept**
Amoebiasis is an infection caused by the protozoan parasite Entamoeba histolytica, which primarily affects the gastrointestinal tract. The disease can manifest as asymptomatic colonization, amoebic dysentery, or extraintestinal amoebiasis.

**Why the Correct Answer is Right**
The most common site for amoebiasis is the cecum, which is the beginning of the large intestine. Entamoeba histolytica trophozoites infect the colonic mucosa, leading to inflammation and ulcers, especially in the cecum and ascending colon. This is due to the parasite's ability to adhere to and invade the colonic epithelium, causing tissue damage and disruption of the mucosal barrier.

**Why Each Wrong Option is Incorrect**
**Option A:** Liver is an incorrect option, as while the liver can be affected in amoebic liver abscess, it is not the most common site for amoebiasis.
**Option B:** Small intestine is less commonly involved in amoebiasis compared to the large intestine.
**Option C:** Rectum can be involved in amoebiasis, but it is not the most common site.

**Clinical Pearl / High-Yield Fact**
Amoebiasis should be suspected in patients with chronic diarrhea, weight loss, and abdominal pain, especially if they have traveled to or live in areas with poor sanitation.

**Correct Answer:** C.