Explanation:

- After three months of practice, I can now swim quite fast.

- Correct answer: Option 3 – can

- "Can" indicates the ability or capacity to do something in the present. Since the person is describing their current ability after practice, "can" is the appropriate choice.

- Option 1 – cannot

- "Cannot" means lacking the ability or capacity. It doesn't make sense here because the person is expressing achievement after practice.

- Option 2 – should

- "Should" implies a suggestion or expectation and is not used to describe ability.

- Option 4 – could

- "Could" often refers to past ability or potential, not present capability.

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