Final answer:
The country located northwest of Iraq with the Euphrates River flowing through it is Syria. Geographically, Syria lies in the Fertile Crescent and benefits from the Euphrates River that originates in Turkey and traverses the region before entering Iraq.
Step-by-step explanation:
The country located northwest of Iraq through which the Euphrates River flows is Syria (A).
Syria is situated in the Fertile Crescent region, a historic area known for early human civilizations and the confluence of the Tigris and Euphrates rivers. These rivers are central to the geography and history of the area, contributing significantly to the region's agricultural prosperity. Presently, water rights of these rivers are of critical importance, especially since they originate in Turkey and flow through countries such as Syria and Iraq, often leading to geopolitical negotiations and conflicts over water resources. Situated to the northwest of Iraq, Syria, in particular, benefits from the course of the Euphrates as it flows from Turkey and into Iraq. This geographic feature establishes Syria as the answer to the question, excluding the other options such as Israel, which is located to the southwest of Syria, Afghanistan, which is far to the east of Iraq, and Islam, which is not a country but rather a major world religion.