The base of the pyramid is built from organisms that primarily
a) are autotrophs.
b) are heterotrophs.
c) consume organisms located above them.
d) are heterotrophic, primary consumers.

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?