Why do countries erect trade barriers that inhibit imports and exports

To protect their local markets and keep a health balance of payments.

Explanation:

They inhibit imports as those require forex and may hurt their own country's production and markets. They inhibit exports at times to prevent shortages of goods they require such as wheat when there is a drought or increases local demand.

sorry but your romanian isn't clear could you just translate to english

explanation:

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.