These are the facet bar graphs for daily average number of passengers arrived at O'Hare by month, from 2017 to 2021?What striking feature is apparent in this graph? What explains this feature of the data?P/S: It might be because of COVID-19. But I don't think that's a statistically right answer

Average Number of Passengers 20,000 - 15,000 - 10,000 5,000 0 Jan Feb 2017 - 2021 Mar Apr 2017 May Jun Jul Aug . Sep Oct Nov Dec Jan Feb _ Mar _ Apr 2018 May. Jun Jul Aug Sep. Average Daily Number of Passengers by month and year Oct Nov Dec Jan Feb Mar _ Apr_ 2019 May _ Month Jun Jul Aug . Sep. Oct Nov Dec Jan " Feb Mar Apr 2020 May Jun Jul Aug . Sep Oct Nov Dec Jan Feb Mar Apr 2021 May Jun Jul Aug_ Sep Oct Nov Dec