In June 2018, a poll asked a random sample of 1000 US adults whether global warming will be a serious problem for the United States. The results show that 51% think global warming will be a very serious problem, 27% think it will be a somewhat serious problem, and 21% think it will not be a serious problem.

(a) What is the sample? What is the intended population? 

(b) Is it reasonable to generalize this result and estimate that 21% of US adults think that global warming will not be a serious problem for the United States?