Which of the following results could lead to a main motion being adopted if the presiding officer votes in favor?

The situation where the presiding officer's vote can shift the outcome of a main motion is crucial in parliamentary procedure. A main motion typically requires a majority vote to be adopted.

In this case, the correct scenario—where the presiding officer votes in favor—occurs when there is a tie in votes, which means there are an equal number of votes for and against the motion. Therefore, if the vote is 20 in favor and 20 opposed, the presiding officer's supportive vote breaks the tie, ultimately resulting in the motion being adopted. This voting dynamic is essential in organizations that follow parliamentary procedure, as it ensures that the presiding officer, who usually remains neutral, can influence the decision in the case of a deadlock.

The other options reflect scenarios where the majority of votes are opposed to the motion, meaning that even with the presiding officer’s vote, the votes cannot reach the required majority for adoption. Thus, they do not lead to the adoption of the main motion, unlike the scenario where the votes are tied, allowing the presiding officer’s vote to have significant impact.