Two years ago this month, a 19-year-old American shot and killed 17 people at Marjory Stoneman Douglas High School in Parkland, Florida. Fourteen of the victims were students； the other three were teachers. The gunman was a former student at the high school.
  On this anniversary, as with other anniversaries of school shootings, Americans continue debating how to make sure students are safe in schools.
  To increase preparedness for such an event, many schools now hold shooter drills（演习）for students and their teachers. A report released by Everytown for Gun Safety, a non-profit organization, notes the possible harmful effects of such exercises. It urges school administrators to look for better ways to make schools safe and to prepare children for an active shooter.
  One problem with the way schools carry out shooter drills is how much they frighten students. When a school fails to inform parents and students about plans for a drill, the children may think that the attack is real. In some communities, the report says, schools deploy individuals who are told to act like "masked gunmen"． Students as young as three or four years old may be told to stay quiet in a small space for a long period of time. Experts on mental health say these experiences can have both short- and long-term effects on how well the children behave in school, as well as on their physical and mental health.
  Melissa Reeves, former president of the National Association of School Psychologists, said the drills may " trigger either past trauma（心理创伤）or trigger such a…reaction that it actually ends up scaring the individuals instead of better preparing them to respond in these kinds of situations."
  In 2007， one study found it better to prepare students for an "intruder"， rather than a shooter. Another study noted the value of announcing drills in advance and following them with discussion. Students in that situation felt better prepared to handle possible violence.



What is the problem with the shooter drills？ ______

A. Students only suffer short-term damage.
B. Students' physical health cannot be affected.
C. Students may think they are real and get scared.
D. Too young children may not understand what is happening.

What does " trigger" in Paragraph 5 most probably mean？ ______

A. Limit.
B. Cause.
C. Reduce.
D. Regulate.

What is Melissa Reeves' attitude toward the shooter drills？ ______

A. Critical.
B. Favorable.
C. Indifferent.
D. Unclear.

How can students be better prepared to handle possible shooter drills？ ______

A. The schools give them a surprise.
B. They only prepare for shooters.
C. The masked "attacker" carries a toy gun.
D. Drills are announced beforehand and discussed afterwards.