The statement most accurately describes this excerpt is that it contains two dependent clauses and one independent clause.
An independent clause is the main clause which is the subject and verb as well as complete as the sentence. However, the dependent clause is incomplete and cannot stand alone.
Therefore, "after a strenuous climb" and "night was approaching rapidly" are dependent clauses that become absolute due to the independent clause that is "hikers decided to make camp before reaching the summit."
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