Who can initiate an optional referendum at the national level?

Congo, Democratic Republic of
Answer
Not applicable
Source
Constitutionof the Democratic Republic of Congo
(Adoptedin 2006, last amended in 20/01/2011)
http://democratie.francophonie.org/IMG/pdf/Constitution_de_la_RDC.pdf
http://www.constitutionnet.org/files/DRC%20-%20Congo%20Constitution.pdf
(Official English translation)
Comment
Constitution providesonly for mandatory referendum.