Final answer:
The sentence that indicates beach erosion is a natural act is " B. These common acts of nature are what leave beaches with less sand," highlighting the role of natural forces in reshaping coastlines. Erosion is a continual process evident in geological structures such as cross-bedding, dunes, and ripples. Option b is the correct answer.
Step-by-step explanation:
The sentence that supports the idea that beach erosion is a natural act is "These common acts of nature are what leave beaches with less sand." This sentence indicates that the process of sand being removed from the beaches is a regular occurrence carried out by natural forces. It is important to understand that erosion is a natural and ongoing process that shapes our coastline by the action of elements like water and wind. Over time, the relentless movement of water — from ocean waves or river currents — transports sediment across various landscapes. Geological evidence, such as cross-bedding in sedimentary rocks, shows us how directional forces like wind and water currents have historically moved materials; thus, beach erosion is part of this continual reshaping of the Earth's surface.
Beach erosion is also depicted in the continuous movement and shaping of dunes and ripples by water or wind, further supporting the idea that erosion is a natural geological process. Dunes are an essential part of the beach ecosystem, often formed and transformed by natural forces, which is implicit in the statement "Dunes are an important part of the natural beach system."
In summary, the natural shifting of sediment, reflected in features like cross-bedding and the topography of dunes and ripples, indicate that beach erosion is a common natural occurrence, an intrinsic part of the geophysical processes shaping the Earth.