A deficient month has 29 days, since the actual lunar cycle is longer but the calendar counts whole days only.
Question 2
In a leap year, what is the order of Adar I and Adar II?
In a leap year, Adar I is full (30 days) and Adar II is deficient (29 days), as ruled in Halacha 5.
Question 3
In a simple year, if there are 4 days between this Rosh HaShanah and the next, what type is the year?
In a simple year: 2 days = deficient, 3 days = regular, 4 days = complete. Four days means a complete year.
Question 4
A year whose Rosh HaShanah falls on Tuesday — what type are its months?
One of the fixed signs: any year whose Rosh HaShanah falls on Tuesday has regular months — whether simple or leap, with no exception.
Question 5
In a simple year whose Rosh HaShanah falls on Thursday — which possibility is excluded?
In a simple year with Rosh HaShanah on Thursday, deficient months are impossible — that would require the next Rosh HaShanah on Sunday, which is not a valid setting day.