题目内容：
根据以下材料，回答题Privacy in the 21st Century
Someday a stranger will read your e-mail without your permission or scan the Websites you've visited, or perhaps someone will casually glance through your credit card purchases or cell phone bills to find out your shopping preferences or calling habits.
In fact, it's likely some of these things have already happened to you. Who would watch you without your permission.0 It might be a spouse, a girlfriend, a marketing company, a boss, a cop or a criminal. Whoever it is, they will see you in a way you never intended to be seen--the 21st century equivalent of being caught naked.
Psychologists tell us boundaries are healthy, that it's important to reveal yourself to friends,family and lovers in stages, at appropriate times. But few boundaries remain. The digital bread crumbs (碎屑) you leave everywhere make it easy for strangers to reconstruct who you are, where you are and what you like. In some cases, a simple Google search can reveal what you think. Like it or not, increasingly we live in a world where you simply cannot keep a secret.
The key question is: Does that matter? For many Americans, the answer apparently is "no".
When opinion polls ask Americans about privacy, most say they are concerned about losing it.
A survey found an overwhelming pessimism about privacy, with 60 percent of respondents saying they feel their privacy is "slipping away, and that bothers me".
But people say one thing and do another. Only a tiny fraction of Americans change any behaviors in an effort to preserve their privacy. Few people turn down a discount at tollbooths (收费站 ) to avoid using the EZ-Pass system that can track automobile movements. And few turn down supermarket loyalty cards. Privacy economist Alessandro Acquisti has run a series of tests that reveal people will surrender personal information like Social Security numbers just to get their hands on a pitiful 50-cents-off coupon (优惠劵) .
But privacy does matter--at least sometimes. It's like health: When you have it you don't notice it. Only when it's gone do you wish you'd done more to protect it.
Why does the author list several cases that your information can be accessed without your permission? A．To introduce the topic.
B．To remind the importance of privacy.
C．To inform what 21 st century is like.
D．To call for the action against the spread of website.
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