题目

Valentine’s Day is named for Saint Valentine, an early Christmas churchman who helped young lovers. Valentine was killed for his Christian beliefs on February 14 more than 1700 years ago, but the day which is named after him is even earlier than that.    More than 2,000 years ago, the ancient Romans celebrated a holiday for lovers. As part of the celebration, girls wrote their names on pieces of paper and put them in a large container. Boys reached into the container and pulled one out. The girl whose name was written on the paper became his lover or sweet heart for a year.    Now, lover 2011年3月10日，云南省德宏州盈江县发生里氏5.8级地震，给人民群众造成了重大损失，因为地震产生的声波属于________，所以地震前人们并没有感知到．倒塌房屋中一些被困人员通过敲击物体使其振动发出声音被获救，说明声音的传播需要________．