An adverb clause is a short sentence or a set of words that will modify a verb as would do an adverb -by explaining why, how, when or where.
In the given sentence, the adverb clause will modify the verb endangered, therefore the clause must refer to it. Options <em>A, B</em> and C, refer to the red panda, meanwhile option <em>D</em> is the only one referring to the mentioned verb.
The right answer is <em>D</em>.
