Answer:
C. Phylogenetic niche conservatism
Explanation:
Based on the information provided within the question it can be said that the term that best explains these "living fossils" is Phylogenetic niche conservatism. This refers to the tendency that a specific species has for retaining certain traits from the ancestors. Which explains why the living "cycads" are nearly identical to fossils.
→ Darwin believed that the need to adapt, in similar words, the changes occruing in the environment caused evolution.
The main cause of evolution, according to Darwin, was natural selection. Natural selection is a process in which a group of organisms with certain characteristics survive and thrive, in comparison to other organisms with different characteristics. This idea basically means that having some characteristics makes you suited for an environment.
And how would that ↑ explain Evolution?
Well, evolution is the change in species that occurs during time. But for you to change, there must be a cause for that change, which is none other than the need to survive, reproduce, etc.
→ As mentioned before, not all characteristics are enough to surive, and hopefully the image pasted below will help you.
Hope it helped,
BioTeacher101