A woman holds her children as she marks the one-year anniversary of the mass kidnapping of more than 200 schoolgirls from a secondary school in Chibok by Boko Haram militants, in Abuja April 14, 2015. Nigeria's President-elect Muhammadu Buhari vowed on Tuesday to make every effort to free the schoolgirls abducted by Boko Haram militants a year ago but admitted it was not clear whether they would ever be found. A march is expected to be held in Abuja on Tuesday to mark the anniversary. REUTERS/Afolabi Sotunde