The answer is Doldrum. In addition doldrum is a belt around the around the Earth near the equator where the sailing ships sometimes get stuck on windless water.
The two main power units for the tectonic cycle are the Sun and the interior of the Earth's core. These affect almost all changes of the lithosphere.
Saint Petersburg has a population of 5 million.
Moscow has a population of 11 million.
Minsk (the capital of Belarus) has a population of 2 million
Kiev (the capital of Ukraine ) has a population of 3 million
So the biggest city of those is Moscow. - a lot bigger than others
The best answer would be letter D. There is no statement in the choices given that would be considered true concerning continental crust. The crust does not contain radioactive elements, and it is lighter and less dense than the mantle. Also, heat transfer goes from crust to mantle.