9 Which level of organization is characterized by a group of cells that work together to perform a common function?
organ
tissue
organ system
organism
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a, i am pretty sure.

weathering - colorado river carves land in arizona to form the grand canyon. cracks form in a sandstone wall surrounding a house. a marble statue near the science museum is changing color due to rainfall

erosion - after a rainstorm, soil and rock piees litter the roadways. the sand dunes in the sahara desert are changing shape.

here's your answer.

a=c and then d= c because of the band so you get ac/dc and you add them together you get sound waves