运营商大数据的4V特征有Volume（体量）、Velocity（速度）、Value（价值密度）、（）。 A: Vaild（有效） B: Visti（拜访） C: Variety（多样）

What is a train ticket -A ________ vaild for a single journey -There are two tyoes of train tickets in Europe First type: train ticket with a reservation -A single ________ document -Assigned train number,time, car number and ________ -Separate train tickets and reservations -________ and a separate reservation -If you can't use reservation portion -purchase a ner separate reservation -board a train on ________ route -board a train that does not require a reservation