• Every natural number is an integer. Every integer is a rational number. We do not consider the zero as a natural number.
• Every rational number has an infinite number of representations by fractions.
• Every rational number has a finite or infinite periodical representation.
• The term “number” means real number.
• There is one-to-one correspondence between the points of the real line and the set of real numbers.

As also understood from the information given, the correct answer is D. The statements regarding to the number sets and the real line in the options I “Every natural number is an integer. Every integer is a rational number.”, II “Every rational number has an infinite number of representations by fractions.” and IV “There is one-to-one correspondence between the points of the real line and the set of real numbers.”are correct. The statement in the option III “Every rational number has a finite periodical representation.” is not correct because of the fact that every rational number has a finite or infinite periodical representation.