Explanation:

GDP (Gross Domestic Product) is the total value of all goods and services produced within a country's borders in a given period. It is one of the most important indicators of economic growth and development. There are different methods to calculate GDP, but the most common one is the expenditure approach, which adds up the value of all final goods and services produced in an economy. Another method is the income approach, which sums up all the incomes generated by the production of goods and services. However, the most straightforward method to calculate GDP is the production approach, which adds up the value of all goods and services produced in an economy.

GVA (Gross Value Added) is the value of output minus the value of intermediate consumption. It is the contribution of an industry, sector, or enterprise to the economy. GVA can be calculated at basic prices or at market prices. Basic prices exclude taxes and subsidies, while market prices include them.

Product taxes are taxes on goods and services, such as VAT (Value-Added Tax) or excise duties. Product subsidies are subsidies on goods and services, such as government grants or price supports. Production taxes and subsidies are similar to product taxes and subsidies, but they are applied to production inputs, such as labor or capital.

Therefore, the formula to calculate GDP (at market prices) is:

GDP = GVA at basic prices + product taxes - product subsidies

This formula includes the value of all goods and services produced (GVA), but it adjusts for the effect of taxes and subsidies on the final prices of products. Product taxes increase the prices of products, while product subsidies reduce them. By subtracting product subsidies and adding product taxes, we obtain the market prices of goods and services.

Option A is the correct answer because it follows this formula. Option B subtracts production taxes and subsidies instead of product taxes and subsidies, which is incorrect. Option C adds production taxes and subsidies to GVA, which is also incorrect. Option D is a general statement that does not provide a specific formula for GDP calculation.