题目内容：

    Would you give your Social Security (安全) Number to the worker at the supermarket? Of course not, right? Yet, if you're like most people, you wouldn't hesitate to give out a different, but equally important number to the same person.

Experts now say that your cellphone number may be more pivotal than any other personal information in the eyes of spammers(垃圾邮件发送者) and identity thieves. In other words, you should guard that cellphone number with your life.

Today, your cellphone number will likely be with you for a very long time. That means if spammers get your cellphone number, it will be much harder to get rid of them. It also means that over the years, your cellphone number will be linked to a lot of personal information from contact lists to bank card numbers, all information that hackers would love to get their hands on.

A few years ago, German security researcher Karsten Nohl showed what he could get using only a person's cellphone number. Califomia Congressman(国会议员) Ted Lieu was given a new cellphone for a day and Nohl was given that cellphone number. Using just that number, Nohl was able to find Lieu's location and movements throughout Los Angeles, read his emails and text messages, and record phone calls between Lieu and his team. And Nohl did all of this from his office in Berlin using just a cellphone number.

Still think it's a good idea to post your number on the Internet?

When you sign up for an account(账户)online, you usually provide your email address and a password. But if you forget that password, many of these companies will send you a password retrieval code(检索码)to your cellphone. Let's say you post something for sale online and you include your name, email, and cellphone number. You've now given a potential(潜在的))thief everything he needs to hack into any of your online accounts. Therefore, it just makes sense to protect yourself by guarding that number as closely as you would guard any other personal information.

1.What does the underlined word "pivotal" in Paragraph 2 most probably mean?

A.Accessible B.Familiar

C.Important D.Manageable.

2.What does the third paragraph mainly talk about?

A.Why people should protect their cellphone numbers.

B.Why people seldom change their numbers.

C.How to protect our personal information.

D.How to get rid of spammers.

3.What did Karsten Nohl's show intend to prove?

A.Nohl is a real expert in hacking.

B.It's necessary to fight against hackers.

C.Lieu's new cellphone has powerful functions.

D.It's easy to hack information through cellphone numbers.

4.What can we infer from the last paragraph?

A.It's a good idea to sell something online.

B.It's necessary to register several accounts online.

C.It's common for people to forget their passwords.

D.It's risky to post your cellphone number online.