To solve the problem, we need to rearrange the letters in the word "TOPS" to form a meaningful word that begins with the letter "O". Let's consider the possibilities:
- The letters in "TOPS" are T, O, P, S.
- The word must start with "O".
By attempting various combinations, we determine:
- The letters "O", "P", "T", "S" don't form a meaningful word when starting with "O".
- However, rearranging them as "STOP" does not satisfy our condition because it starts with "S".
- Rearranging as "SPOT" also doesn't help since it doesn't start with "O".
- Similarly, other combinations like "POST" and "POTS" fail our requirement as they do not start with "O".
Checking all logical combinations that begin with "O" from the available letters, it's evident that:
- "OPTS" can be formed from the letters T, O, P, S.
Since "OPTS" is a valid word meaning a choice or selection, it satisfies the given condition of starting with "O".
Thus, the last letter of the word "OPTS" is "S".
- Since exactly one such word can be formed, our answer is the last letter of this word.
- Therefore, the correct answer is: S.