The twins has studied in this school  ________    .

—What do you think of the book? —It’s ______ a book. It serves as (充当)a really good guide to job hunters.

We should do what we can to save those_________ species, for example, the tiger, an animal which was considered_______ to humans.

— The weather isn’t good enough for an outing , is it？— No. We can’t have _________at this time of the year.

Upon reaching an/a ______  age, children are encouraged, but not forced, to “leave the nest”.