Which of the following are features of Marx's theory of surplus value?
1. It is an extension of Ricardo's theory.
2. Labour power equals the brain, muscle and nerve of the labourer.
3. The value of every commodity is not proportional to the quantity or labour contained in it.
4. The worker must be paid a price proportional to the number of labour hours that entered into its production.
Select the correct answer:

A. 1 and 2

B. 2 and 4

C. 1, 2 and 4

D. 1, 2, 3 and 4

Answer: Option C