Final answer:
The sentence 'If it rains this afternoon, we won't be able to practice' uses conditional mood.
Step-by-step explanation:
The sentence that uses conditional mood is: If it rains this afternoon, we won't be able to practice. Conditional mood is used to express a condition or a hypothetical situation. In this sentence, the condition is 'if it rains this afternoon', and the result of that condition is 'we won't be able to practice'.
Learn more about Conditional mood in sentences