Answer:
D. He began minting coins.
Step-by-step explanation:
Prior to the rule of Orhan gazi, the vast majority of transaction made in ottoman empire was conducted under a bartering system. (a product is exchanged with another product).
This system was flawed because we can't really know the value of a product that is exchanged. So most of the time, it wouldn't really be equal.
In 1327s, The ottoman Empire started to use coin as their main method of transaction. Orhan Gazi'r rule happened between 1324 to 1360 , So this event was occurred under his leadership.