What factor allowed the islamic empire to expand unify and thrive during its golden age

Quran; abbasid armies spread borders; islamic law; Chinese paper making process; House of Wisdom.

b.provides a written record of the transaction

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.