题目

完形填空 It's nineo'clock now. Jane and Helen are in the1. Why are they there?Because this Sunday they want to have a barbecue (户外烧烤) with2friends from school. Theyneed to3some food for the barbecue. There arelots of people in the supermarket. Jane wants some vegetables such as (例如)4and carrots to make a salad. Helen goesto buy some meat. Meat is5for a barbecue. They also buy some6tomake juice.7they get everything, they go to a8store.They like chocolate (巧克力), so they buy a chocolate cake9strawberriesand apples. They think10willbe a great barbecue. （1） A . h火山爆发能产生次声，还有哪些现象能产生次声？（举两例） 人为什么要尽量远离次声源？