How did we feel about the letter's discovery?

The sentiment conveyed by the correct answer indicates that the discovery of the letter was completely unexpected. This suggests a reaction of surprise and perhaps a shift in emotions or thoughts that emerged from encountering something unanticipated. The phrase "a complete surprise" often implies that the individuals involved were not only unprepared for what was revealed in the letter but also likely experienced a strong emotional response due to the unforeseen nature of the discovery.

In this context, understanding that the discovery sparked a reaction contrary to anticipation or prior expectations sets it apart from the other options. Other feelings, such as being expected, overwhelming, or disappointing, imply a level of anticipation or foreseeing the outcome, which would not align with the notion of being taken aback by the discovery. Therefore, recognizing the discovery as a complete surprise captures the essence of a strong and immediate emotional impact that is central to the response chosen.