Final answer:
The best conclusion supported by comparing two photographs is that humans have historically modified their environment to facilitate travel and trade.
Step-by-step explanation:
The conclusion best supported by a comparison of two photographs depicting ancient and modern construction is D) Humans sometimes modify their environment to allow travel and the movement of goods. This is evidenced by the historical practice of altering landscapes to suit human needs, such as draining lakes to build and using sophisticated techniques to construct massive stone structures. Ancient civilizations were innovative with structural designs and would modify natural materials to facilitate activities such as transportation and trade. Over time, they developed trade routes and produced specialized goods that increased economic advantage, further driving the modification of the environment to improve access and efficiency.