The underlined sentence is noun clause. The third option is correct.
The entire sentence is Scientists report that creatures living in the deep sea are in danger of starving to death. The entire dependent clause acts as the object of the sentence, so that it cannot be an adverbial clause. In addition to this, it is not describing or modifying a noun, and therefore it is not an adjectival clause either.
A noun clause is a group of words acting together as a noun. These clauses are always dependent clauses.
The right answer for the question that is being asked and shown above is that: "adverbial clause." The underlined part of sentence 1 is an adverbial clause<span>(1) that creatures living in the deep sea are in danger of starving to death</span>
