The correct answer is option 4, Rousseau. The book "The Social Contract" is a political philosophy work written by Jean-Jacques Rousseau, a prominent French philosopher, writer, and composer. Rousseau`s book was first published in 1762 and is considered one of his most influential works.

To understand the other options, let`s briefly look at them.

- Option 1, Voltaire, is incorrect. Although Voltaire was a notable figure during the Enlightenment era and a philosopher, he did not write "The Social Contract."

- Option 2, Hobbes, is incorrect. Thomas Hobbes was an English philosopher known for his work on political philosophy, particularly his book "Leviathan." "The Social Contract" is not authored by him.

- Option 3, Locke, is incorrect. John Locke was an English philosopher who significantly influenced political thinking. However, he did not write "The Social Contract."

In conclusion, Jean-Jacques Rousseau is the correct author of the book "The Social Contract," which reflects his ideas about the nature of society and government.