阅读理解。
Federal regulators Wednesday approved a plan to create a nationwide emergency alert (警报) system
using text messages delivered to cell phones.
Text messages have exploded in popularity in recent years, particularly among young people. The
wireless industry's trade association, CTIA, estimates (估计) more than 48 billions text messages are sent
each month.
The plan comes from the Warning Alter and Response Network Act, a 2006 federal law that requires
improvement to the nation's emergency alter system. The act tasked the Federal Communications
Commission (FCC) with coming up with new ways to alter the public about emergencies.
"The ability to deliver accurate and timely warning and alters through cell phone and other mobile services
is an important next step in our efforts to help ensure that the American public has the information they need
to take action to protect themselves and their families before, and during, disasters and other emergencies,"
FCC Chairman Kevin Martin said following approval of the plan.
Participation in the alter system by carriers-telecommunication companies-is voluntary, but it has received
solid support from the wireless industry.
The program would be optional for cell phone users. They also may not be charged for receiving alters.
There would be three types of messages, according to the rules.
The first would be a national alter from the president, likely involving a terrorists attack or natural disaster.
The second would involve "approaching threats," which could include natural disasters like hurricanes or
storms or even university shootings. The third would be reserved for child abduction (绑架) emergencies,
or so-called Amber Alerts.
The service could be in place by 2010.
1. What is the purpose of the approval plan?
A. To warn people of emergencies via message.
B. To popularize the use of cell phone.
C. To estimate the monthly number of messages.
D. To promote the wireless industry.
2. The improvement to the present system is in the charge of _____.
A. CTLA
B. the Warning Alert and Response Network
C. FCC
D. federal regulators
3. The carriers' participation in the system is determined by _____.
A. the US federal government
B. mobile phone users
C. the carriers themselves
D. the law of the United States
4. Which of the following is true of cell phone users?
A. They must accept the alert service.
B. They may enjoy the alert service for free.
C. They must send the alerts to others.
D. They may choose the types of messages.
5. An alert message will not be sent if _____.
A. a child loses his way
B. a university shooting happens
C. a natural disaster happens
D. a terrorist attack occurs
6. Which of the following would be the best title for the text?
A. Cell Phone Alerts Protecting Students
B. Cell Phone Alerts by Wireless Industry
C. Cell Phone Alerts of National Disasters
D. Cell Phone Alerts Coming Soon
T0；若撤去电场，只保留磁场，其他条件不变，那么，该带电粒子穿过场区的时间应该是 （ ）
T0
T0
T0
T0
,解得：
,
=
，粒子在磁场中将运动半周，
,选B。