Read the sentence and choose the right option for the gap. They also have parades and more ___ two million people go to see it every year.

The sentence requires a word that indicates a quantity or comparison. 'Than' is used for comparisons, 'at' and 'then' are temporal or locational, and 'of' is a preposition. The phrase 'more than two million' is a common construction to express a quantity exceeding a certain number. Therefore, 'than' is the correct choice to complete the sentence, indicating that the number of people is greater than two million.
Answer: than