Today, land in urban areas typically is used for housing, transportation, and other structures, rather than for agriculture. primanly due to

D.  transportation time and shipping costs being reduced

Explanation:

As a result of advancements in transportation of goods across different areas, getting agricultural produce from rural to urban areas became cheaper and more efficient. This reduced the need for people to have to engage in Agriculture in the urban areas since they could just buy the produce they wanted relatively easily.

This freed up land for other ventures such as more housing, business and sports centres as well as other structures and not forgetting areas reserved for the facilities needed to transport the goods from other areas to urban areas.

no sé si entiendes español pero te daría la respuesta si lo supiera, pero lo siento mucho

i'm sure the answer you are looking for would be

a. an ice age

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