IF I can sing well enough, I'll join the school chorus. The **IF **implies that something is conditional i.e. it may happen, it may not happen (it depends on whether you can sing well enough!) Hope this helps... :)
The correct answer is if i can sing well enough. The other options are already decided, as in they have an answer.
The sentence that implies something may not happen is Option A: 'If I can sing well enough, I'll join the school chorus,' as it expresses a condition that is uncertain. Other options are definitive or questions and do not imply uncertainty. Therefore, this is the only option indicating a possibility rather than a guarantee.
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