Concept:In an ordinary (non‑leap) year, the first day and the last day are the same day of the week because 365 days = 52 weeks + 0 odd days for the year itself (the offset from Jan 1 to Dec 31 is exactly 364 days, a multiple of 7).
Explanation:January 1, 1961 was a Sunday.
1961 was an ordinary year (365 days).
The number of days from Jan 1 to Dec 31 is 364 days, which is exactly 52 weeks.
Therefore, Dec 31, 1961 falls on the same weekday as Jan 1, 1961.
So, the last day of 1961 was Sunday.
Answer:Sunday (Option D)