Circular No. 15/2011/TT-BTNMT dated April 28, 2011 of the Ministry of Natural Resources and Environment amending and supplementing a number of articles of the Minister of Natural Resources and Environment's Circular No. 12/2010/ TT-BTNMT of July 26, 2010, providing the formulation and grant of letter of endorsement and letter of approval for projects under the clean development mechanism within the framework of the Kyoto Protocol