Kate Adie introduces stories from Belarus, Senegal, the US-Mexico border, Cambodia and Brazil. Political prisoners in Belarus attract less international attention than those in Russia - but there are far more of them, even in a smaller country. Many are women, held in a kind of house arrest known as 'chemical detention', under stringent rules which control their every move. Monica Whitlock gathered testimony from some living under these conditions. After months of political turbulence, Senegal eventually did hold its planned presidential election - and the popular vote brought Africa's youngest leader, 44-year-old Bassirou Diomaye Faye, to power. James Copnall reported on the final days of the campaign and reflects on how Senegalese democracy proved itself. Controlling migration to the United States will be one of the most contentious issues in this November's American presidential election. Amid talk of a crisis, and after record numbers of apprehensions of undocumented migrants by the US Border Patrol in December, Tim Mansel visited the border between Mexico and Arizona. Sand might seem as a cheap and almost inexhaustible resource - but far from it. With the world using up more than 50 billion tonnes of it per year, to make everything from skyscrapers to smartphones, reserves could soon run low. In Cambodia there's now a flourishing black market in illegal sand mining along the banks of the Mekong river, as Robin Markwell has seen. And Ione Wells, the BBC's new South America correspondent, explores her new base: the industrial megacity of Sao Paulo. Some people call it 'Rio's ugly sister', but she's found much to appreciate amid its high-rise sprawl.