Which of the following sentence is correct?

ক. "Have you read the latest biography of Indira Gandhi's life?" - This sentence is grammatically correct. It is asking if the person has read the latest biography about Indira Gandhi.

খ. "Do not return back home without completing the work." - This sentence is redundant. "Return back" is repetitive; you can simply say, "Do not return home without completing the work."

ঘ. "If all of us cooperate together, we will succeed." - This sentence is redundant. "Cooperate together" is repetitive; you can simply say, "If all of us cooperate, we will succeed."

In summary, while ক (Indira Gandhi's biography) is grammatically correct, গ (The three brothers had nothing in common) is the correct choice without any redundancy or grammatical issues.