What are research submersibles like alvin useful in studying?

Research submersibles like Alvin are useful in studying because this human-occupied vehicle can collect data throughout the water column, produce a variety of maps, and perform photographic surveys. Alvin's two robotic arms can manipulate instruments and obtain samples ranging from hard-rock geology to delicate biology, and its sampling basket can be reconfigured daily based on the needs of each dive.

the first phase of the government’s plan for settlement was building the transcontinental railroad. the railroad provided a way to bring settlers and manufactured goods west and ship their agricultural and mining produce east. the transcontinental railroad was an essential artery for rapid development of the frontier.

the second phase of the government’s plan was a liberal land distribution policy that made it possible for many people to homestead. with these two key elements—transportation and cheap land—the government rapidly achieved its goal of persuading people to move west, settle on farms, and push back the frontier.