题目内容：

    What's safer? Using a numeric PIN code(数字密码)to unlock your smartphone or relying on a swipe(滑动)pattern? New research suggests that, at least when someone close by could be looking over your shoulder, you might be safer with an old-fashioned PIN.

The research by the United States Naval Academy and the University of Maryland tested what could best secure smartphones from so-called "shoulder surfing attacks". So, if you are worried about someone looking over your shoulder while you unlock your phone, would you be wiser to use a PIN or a pattern? According to this research at least, the answer to that question is pretty clear.

Those who have a single observation of your screen as you unlock it with a swipe pattern will be successful in knowing it 64.2% of the time. Security can be improved somewhat by removing lines on the pattern lock (35.3% success rate for shoulder surfers).

By comparison, the use of a six-digit PIN greatly reduces the chances for an attacker to determine how to unlock your smartphone, with just 10.8% of attacks being successful. In tests, viewers were able to determine the users' lock-screen patterns from up to six feet away, from a variety of different angles, even after a single viewing.

Indeed, when it comes to safety, past research has determined that an unlock pattern is about the same as a three-digit PIN -something I hope that none of us would rely upon.

The researchers' conclusion is that a PIN of six digits or more is the most secure de fence against shoulder surfing attacks, and while both types of pattern lock are poor, patterns without lines provide greater security.

Unsurprisingly, the research confirmed that phones with larger screens were found to provide less security against shoulder surfing attacks.

1.What did the research focus on?

A.What lock-screen patterns people use. B.When shoulder surfing attacks occur.

C.Why people prefer numeric PIN codes. D.How you can unlock your phone safely.

2.What do we learn about shoulder surfing attacks?

A.They can increase our screen time. B.They are a threat to our privacy.

C.They are a kind of physical attack. D.They can be done through remote control.

3.Which of the following proves to be the safest?

A.A six-digit PIN. B.A three-digit PIN.

C.A lock-screen pattern with lines. D.A lock-screen pattern without lines.

4.What does the author intend to do in the last paragraph?

A.Add some background information. B.Provide some advice for the readers.

C.Offer additional topic-related information. D.Summarize the previous paragraphs.