Cannot answer, please provide more information.
This is not an independent clause: it is dependent on the main phrase here, which is "<span>Most of these animals stay under water".
The underlined clause tells us something about why they must stay under water; and sentences that tell us about the why are called the "adverb clauses" - the correct answer.
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I think it might be reflective essay, because you're reflecting on something that already happened.
But you might wanna make sure.
