What is contact metamorphism?

high pressure causes the rocks to change.

subduction causes the rocks to change.

heat from intruding magma causes the rocks to change.

pressure from tectonic plate collisions causes the rocks to change.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.

i think the answer is a.keratin is the pigment responsible for skin color.