Which of the following types of "voice" is most effective in written communication?

In written communication, using the active voice is most effective because it is clear and direct. Active voice makes it easier for the reader to understand who is doing what, leading to less ambiguity. For example, "The manager approved the request" is clearer than "The request was approved by the manager." Reference: "The Elements of Style" by Strunk and White, which advises using active voice for clarity and precision in writing.