Teenagers are warned to be careful when making friends online, because when you can’t see a person, they could be __________.

—Mary，new copies of Harry Potter are on sale now． —Great! Let’s go and buy       this afternoon．

The case of Li Gang became a hot topic and so did ______of Li Tianyi.

—Have you got any books on English grammar? I’d like to borrow       ． —Yes, here you are．But you must return it by Friday．

Can you show me ____ pen?   This one is too expensive.