Select the most appropriate word to fill in the blank.

The ______ part of this issue is that the investigation officer himself turned out to be the culprit.

startling

The sentence is discussing an issue or situation, and it wants to emphasize a specific aspect or quality of that issue. In this context, the word "startling" is the best choice because it conveys the idea that the revelation about the investigation officer being the culprit is surprising and shocking. This word captures the element of unexpectedness and significance in the situation.

Let's briefly look at the other options:

• Option 1: "funniest" - This word implies humor or amusement, which is not suitable for a sentence describing a serious and shocking situation.

• Option 2: "major" - While "major" could work, it doesn't convey the same level of surprise and shock as "startling." It is more neutral and doesn't emphasize the unexpectedness.

• Option 3: "real" - This word doesn't fit the context well because it doesn't add any specific meaning related to the surprise or unexpected nature of the situation.

Therefore, "startling" is the most appropriate word in this sentence to highlight the surprising and unexpected aspect of the issue.