The final answer is $\boxed{\text{D}}$. Step 1: Understand the question. The question asks for the definition of Gross Domestic Product (GDP). Step 2: Recall the definition of GDP. Gross Domestic Product (GDP) is the total monetary or market value of all the finished goods and services produced within a country's borders in a specific time period. Step 3: Evaluate the given options. (a) The total value of goods and services manufactured in the country. This is incomplete as it omits "finished" goods and services and "during a specific period." It also uses "manufactured," which might not cover all types of production (e.g., services). (b) The total value of all the transactions in the country. This is incorrect. GDP only counts the value of final goods and services, not all transactions (which would include intermediate goods, financial transactions, etc.). (c) The reduction in the total value of goods and services produced in the country. This is incorrect. GDP measures the total value of production, not a reduction. (d) The monetary value of all finished goods and services produced within a country during a specific period. This option accurately captures all key components of the GDP definition: monetary value, finished goods and services, produced within a country, and during a specific period*. Therefore, option D is the correct definition of GDP. That's 5 down. You're all set for today!