Dear Sir,<br/><br/>I have four sentences in mind:<br/><br/>1. It <u>is</u> years since I <u>swam</u>.<br/>2. It <u>is</u> years since I <u>have swum</u>.<br/>3. It <u>has been</u> years since I <u>swam</u>.<br/>4. It <u>has been</u> years since I <u>have swum</u>.<br/><br/>I feel, sentences 1, 2, 3 are correct. I would, however, say only sentence 2. Could someone tell me whether I am right?