**Core Concept**
The Mini-Mental State Examination (MMSE) is a widely used, brief, and standardized test for cognitive impairment and to screen for dementia. It assesses various cognitive functions, including arithmetic, memory, and orientation.

**Why the Correct Answer is Right**
The MMSE consists of 30 items, which are divided into five sections: orientation (10 points), registration (3 points), attention and calculation (5 points), memory recall (3 points), and language (9 points). These items evaluate the patient's cognitive abilities, such as their ability to perform simple arithmetic, remember names and addresses, and understand and respond to spoken language. The total score ranges from 0 to 30, with higher scores indicating better cognitive function.

**Why Each Wrong Option is Incorrect**
**Option A:** 10 - This is incorrect because the MMSE consists of more than just orientation, which is only one of the five sections.
**Option B:** 15 - This is incorrect because the MMSE has more items than just the arithmetic and memory recall sections combined.
**Option C:** 20 - This is incorrect because the correct total number of items in the MMSE is 30, not 20.

**Clinical Pearl / High-Yield Fact**
The MMSE is a useful tool for clinicians to quickly assess a patient's cognitive status, but it should not be used as the sole criterion for diagnosing dementia or cognitive impairment. It is essential to consider the patient's clinical history, physical examination, and other diagnostic tests when making a diagnosis.

**✓ Correct Answer: D. 30**