The question is asking the determine the role that the United States do in the ecosystem base on the passage and situation in the question that you have state, base on my research, I would say that its role is a Dominant. I hope you are satisfied with my answer and feel free to ask for more if you have question and further clarification
Answer: [B]: " a muscular foot ".
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"Every mollusk has a head, body, and <u> muscular foot </u> . "
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The answer is Transportation systems can be conceptualized as a set of relationships between nodes, networks, and demand. These relationships include places that spatially express that demand, flows between them, and infrastructure designed to manage and connect those flows. All components of a transportation system are designed to facilitate the movement of passengers, cargo and information, either as separate components or together.
demand. A derived function for the mobility of people, cargo, and information for a variety of socioeconomic activities. Node. Where movements begin, end and pass through (mediation), entry or exit points in a transportation system. They vary according to the geographical scale considered, from local nodes (e.g. a subway station) to global nodes (e.g. port or airport terminals).
networks. Consisting of a set of links expressing the connectivity between places and the capacity to handle volumes of passengers or cargo.Locations. Nodes where demand is expressed as a point of origin, destination, or transit. The level of spatial accumulation of socioeconomic activities (production and consumption) collectively defines demand and where that demand is produced.
streams. The amount of traffic in a network made up of nodes and links. This is collectively a function of demand and the ability of chains to support it.
infrastructures. Means of transportation such as highways and terminals express the physical reality of a network and are designed to handle demand with specific characteristics in terms of volume and frequency. The facilities that provide access to a network are collectively characterized by their centrality and the links they emanate.
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