A、February. B、May. C、July. D、August. B细节题。文章明确提到May is the least criminal month of all，表明五月是犯罪率最低的月份，也就是说五月最安全。故选项B正确。

Crime has its own cycles, a magazine reported some years ago. Police records show a surprising relation between changes in the season and crime patterns.
The pattern of crime has changed very little over a long period of years. Murder reaches its high during July and August, as do other violent attacks. Murder, in addition, is more than seasonal; it is a weekend crime. It is also a nighttime crime: 62 percent of murders are committed between 6 p. m. and 6 a. m. One is most likely to be robbed between 6 p. m. and 2 a. m. on a Saturday night in December, January, or February. Except for one strange statistic, May is the least criminal month of all.
    Apparently our intellectual season cycles are completely different from our criminal patterns. Professor Huntington made a lot of studies to discover the seasons when people read serious books, attend scientific meetings, and make the highest scores on examinations. In all examples, he found a spring peak and an autumn peak separated by a summer low. On the other hand, Professor Huntington’s studies showed that June is the peak month for suicides and for admitting patients to mental hospital. June is also a peak month for marriages!
    Possibly, high temperature and humidity bring on our strange and surprising summer actions, but police officers are not so sure. "There are, of course, no proof of a relation between humidity and murder", they say. "Why murder’s high time should come in the summer time we really don’t know".
Questions:
29. What is the passage mainly about?
30. Which is the safest season?
31. What did Professor Huntington’s research show?