When an initiative proposal and an alternative proposal are put to the vote on the same day, what choices does the voter have?

Political Constitution of Guatemala (Constitución Política de la República de Guatemala) (1985 with amendments in 1993)http://www.constitutionnet.org/files/Guatemala%20Constitution.pdf

Electoral Code (Ley Electoral y de Partidos políticos) http://hablandoguatemala.files.wordpress.com/2011/01/ley-electoral-y-de-partidos-politicos-de-guatemala3.pdf