[单选题]含硫化氢气井发生井喷失控,距井口500米范围内的居民点的硫化氢3分钟平均浓度达到100ppm,存在无防护措施的公众,应在_____分钟内实施点火
A. 10
B. 15
C. 20
D. 30

Sleepwalking is a scientific reality. It’s one of those strange phenomena that sometimes border in the fantastic. What is certain about sleepwalking is that it is a symptom of emotional disturbance, and’ that the only way to care it is to remove their worries and anxieties that eaus6 it. Doctors say that sleepwalking is much more common than is generally supposed. Many sleepwalkers do not seek help and so are never put on record, which means that an accurate count can never be made.
The questions: Is the sleepwalker actually awake or asleep Scientists have decided that he is about half--and--half. Doctors think the sleepwalker is awake in the muscular area, partially asleep in the sensory area. In other words, a person can walk in his sleep, move around, and do other things, but he does not think about what he is doing.
What are the chances of a sleepwalker committing a murder or doing something else extraordinary in his sleep In general
A. Sleepwalking is such a serious social problem that we should make greater efforts to find what cause it.
B. In telling sleepwalking stories, people may invent something extraordinary to be added to them for the purpose of finding an audience.
C. Sleepwalking is a sign that the person has a psychological problem. He worries about and fears for something in life.
D. The American expert on sleep has never seen a sleepwalker walking beyond his own front door. This proves that sleepwalking has no scientific basis of any kind.