Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the question.

Mark Zuckerberg was born in 1984, in New York, into a prosperous, professional family. He developed an interest in computers at an early age and when he was twelve, he created a messaging program which he named "Zucknet". His dentist father used it in his surgery so that his receptionist could inform him of the arrival of a patient without yelling across the room. Together with his friends, Mark spent much of his spare time as a boy designing and making computer games just for fun.

In 2002, Mark enrolled at Harvard University. By his second year at the institution, he had acquired a reputation on the campus as a developer of software. It was at that time he invented "Facemash" which compared pictures of female students and allowed users to vote on which one was the most attractive. The program became very popular on campus, but was later shut down by the university authorities who deemed it 'inappropriate'.

Based on the buzz of "Facemash", three of Mark's fellow students, Divya Narendra, and twins, Cameron and Tyler Winklevoss, asked him to work with them on an idea for a social networking site called "Harvard Connection". This site was designed to use information from Harvard's student networks to create a dating site for the university's elite. Mark was initially enthusiastic about the complex project but boredom soon set in

and he backed out of it to work on his own social networking site. He created a site that allowed users to produce their own profiles, upload photos, and communicate with other people beyond the confines of the university. He called the site "Facebook" and he operated from one small college room until June 2004 when he finally abandoned his studies to devote himself fully to Facebook and moved the company to California. By the end of 2004, Facebook had one million users and Mark was climbing high.

What is the word "backed out of " in paragraph 3 closest in meaning to?