【题目】World No Tobacco Day on May 31st, and scientists have had the term “third-hand” smoke introduced to the public．
A. falls B. fell
C. has fallen D. is falling
在线课程【答案】A
【解析】考查时态。句意：世界无烟日定于五月三十一日。根据句意可知用一般现在时态，World No Tobacco Day是句子的主语，单数第三人称，故答案为A。