Here are the suggested answers for the fill-in-the-blank questions:

20. **urgent** - "While I am on holiday, ring me at my hotel only if there are any **urgent** messages for me."
21. **axe** - "This **axe** is not big enough to cut down a tree."
22. **otherwise** - "He must give us more time **otherwise** we shall not be able to make a good job of it."
23. **grateful** - "I should be very **grateful** if you would post this letter for me."
24. **signs** - "When you get to the motorway, follow the **signs** for London."
25. **extends** - "The garden **extends** as far as the river."