Answer: C. The manatee is a rare animal and it needs our help.
A. It is a rare animal and the manatee needs our help.
It is good to state what the "it" is first.
B. The manatee is a rare animal and needs our help.
This one is good, but what needs our help? The manatee, which in option C, can be referred to as "it."
C. The manatee is a rare animal and it needs our help.
This one is our answer! It combines them without using too many words and states the subject with a pronoun.
D. The manatee is a rare animal and the manatee needs our help.
We do not need to say "The manatee" twice in the sentence as the subject does not change.
Have a nice day!
I hope this is what you are looking for, but if not - comment! I will edit and update my answer accordingly. (ノ^∇^)
- Heather