Answer : 2. "Rhine"
Explanation :

The river that is often referred to as the "lifeline of European trade" is (B) Rhine. The Rhine River is a major waterway in Europe that flows through several countries, including Germany, France, the Netherlands, Switzerland, Austria, and Liechtenstein. It plays a crucial role in the transportation of goods and is an important trade route, earning it the designation as the "lifeline of European trade."