text:  You're listening to NewsHour. Well, four days on from the collapse of a school building during morning classes in Joss in Nigeria's Plateau State, people are trying to come to terms with the tragedy. Officials say 22 children died when the roof of the Saint Academy came down, and many more are being treated in hospital. The Onovo family lost their 16-year-old son, Chidera. BBC's Chris Walker spoke to the victims' mother, father and little sister.