Which version expresses a transformation of regret using "if only"?

The phrase "If only I had tried harder" effectively expresses a sense of regret because it reflects on a past action that was not taken, indicating a wish that the speaker had made a greater effort in a previous situation. This transformation conveys both the recognition of an opportunity missed and the desire for a different outcome based on past choices.

In contrast, the other options do not encapsulate regret in the same way. "If only I had gone" also conveys regret, but it is more specific and does not articulate the speaker's feelings about their level of effort. "If only I could study more" suggests a current limitation rather than reflecting on past actions. Lastly, "If only I studied more" implies a desire to modify current habits without framing it as a past regret, as it presents it as a conditional wish rather than a reflection on missed opportunities. Thus, the first choice distinctly illustrates regret in relation to a past effort.