**Core Concept**
Depression in developing countries often manifests with somatic symptoms, which are physical complaints without a clear medical cause. This phenomenon is known as somatization. It's a common challenge in diagnosing depression in these regions due to the cultural and socioeconomic factors influencing the presentation of mental health issues.

**Why the Correct Answer is Right**
The correct answer, **C. Vague body aches**, highlights the somatic presentation of depression in developing countries. Patients may exhibit a range of physical complaints, including headaches, joint pains, and gastrointestinal issues, without any apparent medical explanation. This somatization is thought to be a coping mechanism for dealing with the stress and emotional turmoil associated with depression. The lack of access to mental health services and the stigma surrounding mental illness may also contribute to the somatic presentation of depression in these regions.

**Why Each Wrong Option is Incorrect**
**Option A:** Low mood is a classic symptom of depression, but it's not the most prominent feature in developing countries. Patients with depression in these regions often present with somatic symptoms rather than the characteristic low mood.
**Option B:** Sleep disturbance is another common symptom of depression, but it's not unique to developing countries and doesn't capture the somatic presentation of depression in these regions.
**Option D:** Suicidal tendency is a severe and serious symptom of depression, but it's not the most prominent feature in developing countries. While suicidal ideation can occur, the somatic presentation of depression is a more distinct characteristic of depression in these regions.

**Clinical Pearl / High-Yield Fact**
In developing countries, depression often presents with somatic symptoms, which can make diagnosis challenging. Clinicians should be aware of this phenomenon and use a comprehensive approach to diagnose depression, including assessing for somatic complaints.

**✓ Correct Answer: C. Vague body aches**