In the given question, a phrase/ idiom has been given and there are three ways in which the word has been used, in similar or different forms. You need to see which of the sentences have correctly used the highlighted phrase/ idiom, and mark that as your answer. Once in a blue moon 1. Ever since she shifted to Chennai, we hear from her once in a blue moon . 2. The man and his wife were separated and only met once in a blue moon on special occasions, or when their children had some news. 3. Once in a blue moon , he would call up his grandfather, and tell him about the goings-on in his life.