Concept:The International Day of Happiness is a United Nations-recognised day observed every year on 20th March.Explanation:The United Nations celebrates this day to promote happiness and well-being as universal goals.For 2023, the official theme focused on mindfulness, gratitude, and kindness.The complete theme was “Be Mindful, Be Grateful, Be Kind”.This matches option C.Answer:C. Be Mindful, Be Grateful, Be Kind