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."

Answer: B) Magnetic north Explanation: Wherever on earth we hold a compass, the needle points towards the magnetic North Pole. A compass is a great tool for navigation. Compass is widely used in aircrafts, ships, military services,...

Answer: B) Strontium Explanation: We know that, Elements in the same group of the periodic table have similar characteristics. Here Magnesium and Strontium shared some similar properties because they both belong to the same group. Sr is the chemical symbol for strontium which is a group two element; it has atomic number of 38.

The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core. There are two types of Shadow zones: one for P waves and one for S waves.   P wave shadows between 104-140 degree, both sides; S wave shadow from 105 of one side to 105 of the other.