**Core Concept**
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline, primarily affecting memory, language, and problem-solving abilities. The disease is associated with the accumulation of amyloid-beta plaques and tau tangles in the brain, leading to neuronal loss and synaptic dysfunction.

**Why the Correct Answer is Right**
Acalculia, which refers to difficulty with mathematical calculations and problem-solving, is not a characteristic feature of Alzheimer's disease. In contrast, aphasia (difficulty with language comprehension and production), agnosia (difficulty recognizing objects or people), and apraxia (difficulty with motor planning and execution) are common cognitive deficits observed in AD patients. These deficits are thought to result from the degeneration of specific brain regions, including the temporal lobes, parietal lobes, and frontal lobes, which are critical for language, spatial processing, and motor control.

**Why Each Wrong Option is Incorrect**
**Option A:** Aphasia is a common symptom of Alzheimer's disease, resulting from the degeneration of language processing areas in the brain. It can manifest as difficulty with word-finding, comprehension, or repetition.
**Option C:** Agnosia, or difficulty recognizing objects or people, is also a characteristic feature of Alzheimer's disease. It can result from the degeneration of the temporal lobes, which are critical for object recognition and spatial processing.
**Option D:** Apraxia, or difficulty with motor planning and execution, is another common symptom of Alzheimer's disease. It can result from the degeneration of the frontal lobes, which are critical for motor control and planning.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Alzheimer's disease is a heterogeneous disorder, and not all patients will exhibit all of these cognitive deficits. However, the presence of aphasia, agnosia, and apraxia can be indicative of AD, particularly in the later stages of the disease.

**✓ Correct Answer: B. Acalculia. Acalculia is not a characteristic feature of Alzheimer's disease.**