The Danube river is one of the largest and most important rivers in Europe, this river originates in Germany and crosses multiple countries including Austria, Hungary, Croatia, Romania, and Ukrania. On the other hand, the map presented shows three important rivers located in Russia that include the Volga (Number 1), the Ob (Number 2) and the Lena (Number 3). This means all the Volga, Ob and Lena rivers are labeled in the map presented but not the Danube as this is located in Germany and other countries southern Russia.
The three rivers shown are the Volga 1, Ob 2 and Lena 3 all in Russia and the Danube is not shown because it is not in Russia but flows in behind the Adriatic Sea over to Germany and so is in a different part of Europe though all 4 rivers are major rivers in Europe.
