Correct Option: D

National Income is defined as the sum total of all the goods and services produced in a country, in a particular period of time. Normally this period consists of one year duration, as a year is neither too short nor long a period. National product is usually used synonymous with National income. Alfred Marshall in his ‘Principle of Economics’ (1949) defines National income as “The labour and capital of a country, acting on its natural resources, produce annually a certain net aggregate of commodities, material and immaterial, including services of all kinds…..and net income due on account of foreign investments must be added in. This is the true net National income or Revenue of the country or the national dividend.” So the inocme of watchmen will be included while computing it.