1I alone is sufficient while II alone is not sufficient
2II alone is sufficient while I alone is not sufficient
3Either I or II is sufficient
4Neither I nor II is sufficient
From I, we conclude that 5th, 12th, 19th and 26th of March, 2006 were Sundays.
So, the last Sunday fell on 26th.
From II, we conclude that 31st March, 2006 was Friday. Thus, 26th March, 2006 was the last Sunday of the month.