Read the sentence. college applicants need to understand whom they must . which correctly identifies the clause in this sentence? adjective clause modifying the noun noun clause as object noun clause as compliment noun clause as subject

Assuming the clause you are referring to is whom they must please, the correct answer is noun clause as object.
Objects are relatively easy to locate in a sentence - just ask the question Who? or What? In this case, you can ask - What do college applicants need to understand? And the object would be - whom they must please. Given that the option object goes only with the noun clause, that would be the correct answer.