Proof is defined as ….. the percentage by volume of alcohol in ethanol-water mixture.

Options

A. Twice
B. Thrice
C. Half
D. Four times

Explanation

To solve the question regarding the definition of proof in relation to the percentage by volume of alcohol in an ethanol-water mixture, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Proof**:
- Proof is a term used to quantify the strength of an alcoholic beverage. It is defined as a measure of the percentage of alcohol (ethanol) in a mixture.

2. **Identify the Relationship Between Proof and Alcohol by Volume (ABV)**:
- In the United States, proof is defined as twice the percentage of alcohol by volume (ABV). This means if a beverage has an ABV of 40%, its proof would be 80.

3. **Apply the Definition to the Given Question**:
- The question states that proof is defined as the percentage by volume of alcohol in an ethanol-water mixture. Based on the US definition, we can conclude that proof is indeed twice the ABV.

4. **Select the Correct Option**:
- Given the options: twice, half, four times, and the context of the question, the correct answer is "twice." This aligns with the definition that proof is twice the percentage of alcohol by volume in the mixture.

### Final Answer:
- The correct answer is **twice**.

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