我的回答是:
a) alcohol is more elastic than pepsi because there are more substitutes for pepsi such as coke, 7up ect
b)natural gas over the next 5 years is more elstic because in the short-run people would still purchase gas (maybe less than the amount they would normally pump in their cars), but in the long-run they would start taking public transportations / moving closer to work ect
b)doors cd is more elastic than all other rock cds because doors cd is a narrower market than the market for all rock cds, and narrow markets tend to have more elastic demand than broadly defined markets since its easier to find close substitutes for narrwly defined goods
d)doritos is more elastic than food,due to the same reason as in part c