Which question would be asked in a dichotomous key

the answer is b. because you, yourself can physically can see it.

compost can be added to topsoil as a:

pesticide

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.