Modern cell theory is best described as being based on
a) similar evidence collected in multiple experiments by different people
b) experiments conducted in the mid-1600s
c) accounts of what does and does not happen in the natural world
d) the work of robert hooke

A) similar evidence collected in multiple experiments by different people

Hope this helps!

If there is no reason to change (constant climate), then change won't occur. For example, a desert is basically always dry and hot with sand and few clouds. If a creature is fit for the climate, it will continue to exist until a severe enough climate change. For a real world example, in pre-industrial Europe, the birch trees were white. This permitted white moths to survive and not get eaten by the owls that hunt them, until the industrial revolution. Ash got on the birch trees, changing the color of the trees to a darker black. The white moths stood out, and therefore got eaten, permitting the black variant of the moths to thrive, where they were close to complete eradication before the revolution.