**Core Concept**
The question is testing the clinical manifestations of mania, a key feature of bipolar disorder. Mania is characterized by elevated mood, increased energy, and decreased need for sleep, often accompanied by impulsivity and poor judgment.

**Why the Correct Answer is Right**
The correct answer is **flight of ideas**. This is a hallmark symptom of mania, where patients rapidly switch between different thoughts, ideas, or topics, often without logical connections. This is thought to be related to an overactive prefrontal cortex and excessive dopamine release in the brain. The patient may exhibit rapid speech, jumping from one topic to another, and may appear distractible or easily sidetracked.

**Why Each Wrong Option is Incorrect**
**Option A:** Pressure of speech is a feature of mania, but it is not as specific or characteristic as flight of ideas. Pressure of speech refers to speaking rapidly and with increased volume, but it can also occur in other conditions such as anxiety or schizophrenia.
**Option B:** Grandiosity is a common feature of mania, but it is not a specific clinical sign. Grandiosity refers to an exaggerated sense of self-importance or achievement, which can be seen in various psychiatric conditions.
**Option C:** Agitation is a feature of mania, but it is not as specific as flight of ideas. Agitation refers to restlessness, pacing, or other signs of physical tension, which can occur in various conditions such as anxiety or schizophrenia.

**Clinical Pearl / High-Yield Fact**
To remember the key features of mania, use the mnemonic "FAD": Flight of ideas, **A**ctivity (increased energy), and **D**isinhibition (impulsivity and poor judgment).

**Correct Answer:** C. Agitation