The correct answer is option 4, Damascus. Damascus is widely believed to be the oldest continually inhabited city in the world. The city has a long history, dating back to at least the third millennium BCE. It has served as a significant cultural, economic, and political center throughout the ages.

Option 1, Jerusalem, is also an ancient city with a rich history, but it is not the oldest continually inhabited city. Option 2, Baghdad, was founded in the 8th century CE and option 3, Istanbul, was founded in the 7th century BCE as Byzantium before being refounded by the Romans as Constantinople.

It is important to note that the status of the oldest continuously inhabited city can be subject to debate, as different sources may provide slightly different information.