CORRECT answer is 'through a LONG struggle'.Let's look at the following statement from the passage:'The goal of INDEPENDENCE was achieved in India through a prolonged struggle, during which, the far-sightedness of the leaders of the freedom movement resulted in giving a final shape to our social and ECONOMIC goals to be achieved after freedom.' Through the above-mentioned statement, it is evident that Independence in India was achieved through a long struggle.Hence, option 3 is the correct answer.Prolonged means continuing for a long time or longer than usual or lengthy.For eg.- The region suffered a prolonged drought.