The correct answer is (a) Vienna Convention.
The Vienna Convention on the Law of Treaties is an international treaty that codifies the customary international law regarding treaties. It was adopted on 23 May 1969 and entered into force on 27 January 1980. The Convention has 119 parties.
Article 39 of the Vienna Convention provides that a treaty may be amended by agreement between the parties. Article 40 provides that a treaty may be modified by subsequent practice in the application of the treaty establishing an agreement between the parties regarding its interpretation or application.
The Durban Convention is a protocol to the United Nations Framework Convention on Climate Change. It was adopted on 11 December 2011 and entered into force on 15 January 2012. The Convention has 197 parties.
The Desertification Convention is an international treaty that aims to combat desertification and mitigate the effects of drought. It was adopted on 17 June 1994 and entered into force on 26 December 1996. The Convention has 196 parties.
The Johannesburg Convention is a protocol to the United Nations Framework Convention on Climate Change. It was adopted on 9 December 2002 and entered into force on 11 September 2005. The Convention has 195 parties.
The Vienna Convention is the most relevant convention to the question of amendment and modification of treaties because it is the most comprehensive and authoritative codification of international law on this topic. The Durban Convention, the Desertification Convention, and the Johannesburg Convention are all important treaties, but they do not specifically address the issue of amendment and modification of treaties.