Correct option is A
Given that the 20th day is the 4th day before Monday, we establish that the 24th is a Monday.
With a weekly cycle, we backtrack 7 days at a time to find other Mondays in the month, placing them on the 17th, 10th, and 3rd.
From this pattern, if the 3rd is a Monday, then the 1st of the month falls two days prior, making it a Saturday.