Hand washing has external health benefits, prevent the spread of communicable diseases. if a program were somehow devised so that people received a small reward every time they washed their hands, we would expect the frequency of hand washing to and the number of people who are sick to .

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.