To be considered sovereign, the state must
a. control its borders.
b. hold supreme and absolute power within its territory.
c. pay taxes to a larger state.
d. maintain complete control of its economy

The best answer is B.

A sovereign state is one which is independent in its own territory and is complete in itself. This means that it neither answers to nor shares power with others, including religious or other government powers. A sovereign state may conduct its own affairs without hindrance or interference.

In order to be recognized as a sovereign state, the state must also have a real and defined territory and must have a permanent, recognized  population as well.

this means that germany had to pay the allied countries. reparations are/is essentially payment for something that they have done wrong, so after ww1, germany was forced to pay reparations so they could replenish the allied countries resources' that they had lost during the war.