1. I expect it to be quite an ordeal.

2. Their concern seems to be unwarranted.

3. I am going to be a doctor in the future.

4. Ben isn't my classmate. （改为肯定句）

5. The paintings are beautiful. （改为否定句）

6. We are friends. （改为一般疑问句）

7. The girls are in the library. （对画线部分提问）

8. Lily's new pencilcase is pink. （对画线部分提问）

9. She is very certain about her decision.

10. He is guessing the outcome of the game.

这些句子展示了"to be"动词在不同语境下的用法，包括表达预期、情感、状态、计划、推测等。