Which of the following countries joined SAARC in the year 2007?

The correct answer is Afghanistan.

The South Asian Association for Regional Cooperation (SAARC) is a regional intergovernmental organization and geopolitical union of states in South Asia.
It was established on December 8, 1985, in Dhaka, Bangladesh, by seven founding member countries: Bangladesh, Bhutan, India, the Maldives, Nepal, Pakistan, and Sri Lanka.

Afghanistan was admitted as the eighth member of SAARC during the 14th SAARC Summit held in New Delhi, India, in April 2007. Therefore, Afghanistan is the country that joined SAARC in the year 2007.