Easy. Answer is oxygen because it says which one was missing before any life was on earth. And in order to have life on earth you need oxygen!
:)
Answer:
Cellular respiration moves carbon from the atmosphere to geosphere.
The<span> duodenum is the first segment of the small intestine</span>
Answer:
B.soil that is frozen solid all year
C.summer thaws combined with frozen permafrost
D.the overflow of a large lake each summer
Answer:
A
Explanation:
when light is limited photosynthesis will be slowed so the euglena will prefer to ingest food...light is needed for photosynthesis