A) They are exposed to high levels of erosive forces.
B) They are exposed to great climatic variation.
C) The crusty nature of the soil is largely the work of filamentous cyanobacteria.
D) Humans have had little impact on the soil conditions.

A) Plants take in simple chemicals, which they synthesize into larger molecules; animals take up larger, more complex molecules.
B) Plants need to take in nitrogen-containing molecules, but animals do not.
C) Plants take in complex molecules; animals take up relatively simple chemicals and synthesize larger molecules.
D) Plants must absorb all 20 amino acids, whereas animals are able to synthesize all amino acids.

A) more; more
B) more; less
C) less; more
D) less; less