Due to their inability to produce enough food to support their population, greek city states formed to help supply the mainland with resources.

Colonies.

Explanation:

Greek colonization was the establishment of new Greek settlements outside the original Greek territory. It took place in two main waves: about 1100 - 900 and then 754 - 535 BC. The reasons for the colonization were, among other things, the overpopulation of the Greek coast, the lack of arable land and food, and the need to protect trade routes and outlets.

On the one hand, colonization supported the spread of Hellenism and the rise of Greek trade. On the other hand, there has been an influx of cheap goods and food to the Greek mainland and a mass decline of the Greek poleis population into debt slavery, which has led to an increase in social tensions.

d is the right answer