When he turned 60, John decided to pursue his dream of writing a novel that had been ______________ for a long time.   lurid  dormant cogent copious

The correct answer is "dormant". This is because the word "dormant" means something that is not currently active but has the potential to become active, which fits the context of the sentence. John's dream of writing a novel was not active (it was dormant), but when he turned 60, he decided to pursue it.

The other options do not fit the context of the sentence. "Lurid" means shocking or sensational, "cogent" means clear, logical, and convincing, and "copious" means abundant in supply or quantity. None of these words accurately describe a dream or idea that has been inactive but is now being pursued.