Final answer:
The proportion of smoking among 18- to 25-year-olds in the United States tends to decline over time.
Step-by-step explanation:
The proportion of 18- to 25-year-olds who are smokers in the United States varies depending on the data source. However, according to the information provided, we can estimate that the proportion is likely to be lower than in previous years.
In Australia, the proportion of smokers among men and women has decreased from 43% and 33% in 1976 to 16.9% and 12.1% in 2014-15 respectively. In the United Kingdom, two-thirds of smokers want to quit, and in Australia, 73% of smokers have tried to give up smoking.
Although specific data for the United States is not given, it is likely that the proportion of smokers among 18- to 25-year-olds has also decreased over time.