Answer:
A. Primary Economic Activities
Explanation:

The Correct choice is : C. <u>Solids</u>
Sound waves need a medium to propagate, and the most suitable medium for that is solids, where it travel the fastest or with greatest efficiency.
Vienna, Austria is the answer.
The answer to this problem would be that the central government and the state governments influence each other in a federal system. A central government would be most likely to be a characteristic of a unitary state while on the other hand, the state governments would be in a federal form of government which resides on the country subdivision. At which as to how they are influencing each other, they may come in terms of domestic policy because it might go to show that the central government and the state governments' interests and other needs be parallel to each other or might even overlap each other.
Answer:
External and Internal forces.
Explanation:
The earth's relief forms such as Mountains, Rivers, Plateaus etc, are changed because of the action of internal and external forces for example; wind, water or human activities.