1. The younger you are, _______ it is to learn.
2. _______ porpoises and dolphins, whales are mammals.
3. The Romans used central heating systems very much like_______.
4. The higher one rises in the atmosphere, _______ the temperature generally becomes.
5. Nerve cells, or neurons, _______ in the human body.
6. The United States spends more money on advertising_______ country in the world.
7. The rooms in the front_______ noisier than those in the back.
8. A microscope can reveal vastly_______ detail than is visible to the naked eye.
9. _______plants, which manufacture their own food, animals obtain nourishment by acquiring and digesting their food.
10. Of all the candidates, Peter is probably_______
11. These two girls_______ that I can't tell them apart.
12. This house is_______ the others we've seen.
13. Apart from Pluto, the outer planets_______ the inner planets and are made mainly of lighter materials such as hydrogen and helium.
14. This is_______ man of all I've been known.
15. _______ we finish the project, _______ we can start the next one.
16. That child behaves_______ of all
17. It is_______ that I have read it twice.
18. For many children, nothing seems so exciting_______ their first airplane ride.
19. A baby might show fear of an unfamiliar adult, _______ he is likely t smile and reach our to another infant.
20. The deep oceans contain some of the_______ of all living creatures.