Deductions & credits

Got it @pk . 

1. So for 'Current Immigration Status' in 1b for 2018, 2019, and 2020 - I should enter F-1 as I was on F-1 all these years?
2. While for 2021, since my H1B started on Oct 5th, 2021 
   1. what would be the date of change in field 1b? Day 1 of H1B or the day before that? 

   2. Also since I was in the country the whole year in 2021 - 4a (days of presence) would be 365 but 4b (days I can exclude) would be number of days till Oct 4th, right?