Each statement in the question provides details regarding the political parties in India, which are dissected below:

I. "The Representation of the People Act, 1951 provides for the registration of political parties." This statement is correct. The act outlines the procedures for registering political parties.

II. "Registration of political parties is carried out by the Election Commission." This is also correct. It is the responsibility of the Election Commission to register political parties in India.

III. "A national level political party is one which is recognised in four or more States." This statement is correct. According to The Election Commission of India, a party is deemed national if it is recognized in four or more states.

IV. "During the 1999 general elections, there were six National and 48 State level parties recognised by the Election Commission." This statement is correct as well.

Therefore, the all above statements are correct so, correct answer is option 4, which includes all the statements (I, II, III, and IV).