Which type of cost occurs when an individual pays for a piano lesson instead of going to a movie?
a) fixed cost
b) marginal cost
c) residual cost
d) opportunity cost

i dont know if its a cause i did it on usatestprep and it said it was d

the correct answer is the following is a list of inventions made in the medieval islamic world, especially during the "islamic golden age" (8th to 13th centuries),[1][2] as well as the late medieval period, especially in the emirate of granada and the ottoman empire.

science and technology in the islamic world adopted and preserved knowledge and technologies from contemporary and earlier civilizations, including persia, india, china, and greece-roman antiquity, while making a number of improvements and innovations.