Passengers walk past posters themed "M Subway-Library" in subway Line 4 in Beijing, capital of China, Jan. 19, 2015. Subway Line 4 passengers can read e-books by scanning the QR code with cellphones in the carriages. As Beijing's first underground library, "M Subway-Library" is a non-profitable project sponsored by Beijing MTR Corp and the National Library to select and recommend 10 books for free online reading yearly.