A、to chase the thieves if it is safe. B、to use credit cards as much as possible. C、to be more careful of where they place their

WOMAN: Good afternoon, Mr Gray. Thanks for coming to our university to talk about the problem in the Darlinghurst area to our new international students.
MAN: Yes. Thank the university to allow me to come to talk to you all afternoon. The reason for my visit here is to outline a problem that female international visitors and students have been having in the Darlinghurst area.
WOMAN: We all heard that for the last month or so, thieves have targeted the area snatching handbags and backpacks from unsuspected women. Why in the Darlinghurst area?
MAN: As you probably know. Darlinghurst is very popular with tourists for shopping and sightseeing and it’s also a popular meeting meeting place for students. There are lots of cafes and coffee shops and unfortunately, we have had some thieves taking advantage of these conditions.
WOMAN: Can you tell us about the thieves more specifically?
MAN: Sure. The thieves are young and fit. They grab the bag from the woman’s shoulder or out of her hand when she’s involved with something else, you know, deep in conversation or window-shopping, so they grab the bag and then run away very quickly. By the time the victims realize what’s happened, the young man’s out of sight and there’s little hope of catching him.
WOMAN: You mean the thieves usually attack female by themselves?
MAN: They used to. But now it seems they’re becoming braver arid targeting women in groups. Age doesn’t seem to matter to the thieves, it’s just a matter of opportunity. They look for someone who isn’t consciously protecting their bag and for a place with an easy getaway, you know, not too crowded.
WOMAN: Are any of these thieves caught?
MAN: We’ve only had two of these bag-snatchers almost caught when the victims chased after them. Unfortunately, on both occasions, as soon as the women reached the thief, he threw the bag right at them and then escaped.
WOMAN: Mr. Gray, can you give the students some suggestions to protect themselves from these brazen thieves?
MAN: Yeah. We don’t encourage you to chase these thieves because we don’t want to see anyone get hurt. So, what can you do? Well, unfortunately, not much but we are asking that you be aware of this danger. If possible, hang onto your bags carefully and never leave your bags on the ground at one of the many cafes when you have a coffee or a meal and don’t leave it on a chair or table-top even if you think it is in your sight. We also caution you about carrying anything too valuable in your bags. It seems like the thieves arc not only after cash. They’ve been using credit cards illegally on the Internet m purchase goods or access pornographic sites. So it is vital that you keep your credit card details and report to the police if it is stolen.
Questions:
19.What is the problem that Mr. Gray describes to the students?
20.Why is it difficult to chase the thieves?
21.How many thieves have the police caught?
22.Which of the following does Mr. Gray suggest the students to do?