Rewrite the following sentences by adding words from the parentheses. Replace the modal verb can (could) with the expression to be able to if necessary.
1. I can give you my book for a couple of days (after I have read it).
2. He can ski (for ten years).
3. We knew that she could swim (since a child).
4. You cannot take part in this serious sport competition (until you have mastered good skills).