Depreciation is a concept in accounting that refers to the reduction in the value of an asset over time due to wear and tear, obsolescence, or other factors. It is a non-cash expense that is deducted from the revenues of a business to reflect the decrease in the value of its fixed assets.

Among the given options, the one that includes depreciation is option 'A' - GNP (Gross National Product) at market price.

Here is a detailed explanation of each option:

a) GNP at market price:
- GNP is the total value of all final goods and services produced by the residents of a country within a specific time period, typically a year.
- GNP at market price includes the market value of all goods and services produced, including the depreciation of fixed assets. It takes into account the value of the final products as well as the depreciation of the capital used in their production.

b) NNP at market price:
- NNP (Net National Product) is the total value of goods and services produced by the residents of a country after deducting the value of depreciation.
- NNP at market price is calculated by subtracting depreciation from GNP at market price. It reflects the net value of goods and services produced, excluding the depreciation of fixed assets.

c) NNP at factor cost:
- NNP at factor cost is the total value of goods and services produced by the residents of a country after deducting the value of depreciation, indirect taxes, and adding subsidies.
- It is calculated by subtracting depreciation and indirect taxes from GNP at factor cost and adding subsidies. It represents the net value of goods and services produced at the cost of factors of production (labor, capital, etc.).

d) None of these:
- This option is incorrect as depreciation is included in GNP at market price (option A).

In summary, depreciation is included in GNP at market price (option A). It is deducted to calculate NNP at market price and further adjustments are made to calculate NNP at factor cost.