**Core Concept**
Achalasia cardia is a primary esophageal motility disorder characterized by the failure of the lower esophageal sphincter (LES) to relax, leading to impaired esophageal emptying. This results in dilatation of the esophagus, and the presence of food residue, which can be visualized on radiological studies.

**Why the Correct Answer is Right**
The classic radiological findings in achalasia cardia include a dilated esophagus, a bird's beak appearance of the distal esophagus, and the presence of food residue. The dilated esophagus is a result of the failure of the LES to relax, allowing food to accumulate and causing the esophagus to stretch. The bird's beak appearance is due to the narrowing of the distal esophagus at the level of the LES.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a characteristic radiological finding in achalasia cardia. However, it may be seen in other esophageal disorders, such as esophageal stricture or esophageal cancer.
**Option B:** This option is incorrect because it is a characteristic radiological finding in achalasia cardia. The dilated esophagus is a hallmark of the disease.
**Option C:** This option is incorrect because it is not a characteristic radiological finding in achalasia cardia. However, it may be seen in other esophageal disorders, such as esophageal diverticula.
**Option D:** This option is incorrect because it is a characteristic radiological finding in achalasia cardia. The bird's beak appearance is a result of the narrowing of the distal esophagus at the level of the LES.

**Clinical Pearl / High-Yield Fact**
Achalasia cardia is often associated with a "bird's beak" appearance on barium swallow studies, which is a result of the narrowing of the distal esophagus at the level of the LES. This is a classic radiological finding that should raise suspicion for achalasia cardia.

**Correct Answer:** D. The correct answer is not provided in the original question, so I will assume it is D. A: This would be incorrect, B and D are correct radiological features of achalasia cardia.