Changes in the trilobite exoskeleton can be attributed to
a.
changing environments
c.
inter-species mating
b.
competition for survival
d.
both a and b

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

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.