In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What are digital albums?, Context: In 2014 artist Jack White sold 40,000 copies of his second solo release, Lazaretto, on vinyl. The sales of the record beat the largest sales in one week on vinyl since 1991. The sales record was previously held by Pearl Jam's, Vitalogy, which sold 34,000 copies in one week in 1994. In 2014, the sale of vinyl records was the only physical music medium with increasing sales with relation to the previous year. Sales of other mediums including individual digital tracks, digital albums and compact discs have fallen, the latter having the greatest drop-in-sales rate.
mediums

Who practices SODIS?, Context: Solar water disinfection (SODIS) involves exposing water-filled plastic polyethylene terephthalate (PET) bottles to sunlight for several hours. Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions. It is recommended by the World Health Organization as a viable method for household water treatment and safe storage. Over two million people in developing countries use this method for their daily drinking water.
Over two million people

Who did others look to to hear about the new system?, Context: Although little was officially announced by Chinese authorities about the signals of the new system, the launch of the first COMPASS satellite permitted independent researchers not only to study general characteristics of the signals, but even to build a COMPASS receiver.

authorities