Answer:
Substrate. The substrate is the surface on which the river organisms live. It may be inorganic, consisting of geological material from the catchment area such as boulders, pebbles, gravel, sand or silt, or it may be organic, including fine particles, leaves, wood, moss and plants.
Explanation:
probably A but I'm not sure about it
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics.
Bonds issued by the U.S. treasury are back by the federal reserve and claim to have no credit risk. Agency bonds also usually have low credit risk. otherwise you just have to look at the bond before you invest and find out what dink of credit risks are involved.
