Final answer:
The correct sentence is option A: Washington said this about the war for independence: "Our cause is noble, it is the cause of all mankind." The correction is to add a comma after the word "noble" to separate the two independent clauses.
Step-by-step explanation:
The correct sentence is option A: Washington said this about the war for independence: "Our cause is noble, it is the cause of all mankind."
In this sentence, the correction is to add a comma after the word "noble" to separate the two independent clauses.
This correction is necessary because the sentence contains two complete thoughts ("Our cause is noble" and "it is the cause of all mankind") that are joined by a coordinating conjunction ("and").