Interest is as______ to learning as the ability to understand, even more so. 

Not everyone has realized what_______ important part the balance of________ nature plays in their life.

After a long vacation, Mike came back _________.

The second half of his voyage was __________ dangerous part, during which he sailed round the Cape Horn.

His health is improving day by day. It is quite ______ that the medicine has a good effect on his disease.