The correct answer is
“Sea mountains form a thriving ecosystem of underwater plants and animals, some of which have never been documented by scientists.”
Depending on the sentence, a pronoun should be placed before or after the verb. In a statement, it will be before, such as in "I can buy a necklace." In a question, it will be after, such as in "Can I buy a necklace?" (which is after the helping verb but before the acting verb)
In the first sentence, the "he" is a nominative as it is a subject.
In the second sentence it is an object as the form "me" is actually "I", but "i" is a nominative form and "me" is an objective form.
In the third sentence "Us" is also used in objective form as "us" is an object of an action by "my sister".
The answer is it adds some unexpected hope by showing that people create beauty even amid poverty.
