Australian embryologists have found evidence that suggests that the elephant is descended from an aquatic animal, and its trunk originally evolving as a kind of snorkel.

(A) that suggests that the elephant is descended from an aquatic animal, and its trunk originally evolving
(B) that has suggested the elephant descended from an aquatic animal, its trunk originally evolving
(C) suggesting that the elephant had descended from an aquatic animal with its trunk originally evolved
(D) to suggest that the elephant had descended from an aquatic animal and its trunk originally evolved
(E) to suggest that the elephant is descended from an aquatic animal and that its trunk originally evolved

I have a few questions:

What is "is descended" construction, has descended present participle.

Secondly for A the OG says that sentence after and is not parallel. The and there is after a comma, making it an independent clause which per my understanding doesn't need to be parallel, it lacks a verb so making it a run on sentence (evolving is not a verb because it is not preceeded with a to be verb).

In Choice C the OG says with cannot be followed by an independent clause, what does it mean by that.

Lastly the OA is E, which has a to suggest an infinitive. What is the rule for using infinitives?