**Core Concept**
The question tests the legal limit of blood alcohol concentration (BAC) for driving, which is a critical safety measure to prevent accidents caused by intoxicated drivers.

**Why the Correct Answer is Right**
The legal limit of BAC is typically set at 0.08% in most countries, including the United States. This means that if a person's BAC exceeds 0.08%, they are considered impaired and can be held liable for any accidents that occur while driving. The BAC is determined by analyzing a breath or blood sample, which measures the amount of alcohol present in the body. The primary enzyme responsible for metabolizing alcohol is alcohol dehydrogenase, which converts ethanol into acetaldehyde.

**Why Each Wrong Option is Incorrect**
* **Option A:** A BAC of 0.05% is considered the legal limit in some countries, but it is not the standard limit in the United States. This option is incorrect because it does not reflect the standard legal limit in the country where the question is likely to be administered.
* **Option B:** A BAC of 0.10% is above the legal limit and can lead to severe impairment. However, it is not the specific limit mentioned in the question.
* **Option C:** A BAC of 0.06% is below the legal limit, but it can still impair a person's ability to drive safely.

**Clinical Pearl / High-Yield Fact**
It's essential to note that BAC can continue to rise after drinking has stopped, due to the body's continued metabolism of alcohol. This is known as the "lag phase" and can last for several hours.

**Correct Answer: D. 0.08%**