D. single- and simple multi-celled organisms
Although more complex animals like invertebrates and multi-celled organisms began to appear, it was very late compared to the original, simpler organisms for which the Precambrian time is characterized by.
Answer:
R. The state of atmosphere at any particular time
Explanation:
Other answers don't seem applicable
A, B and D are the green house gases
D I think hope it's correct for u :)