In a survey of 2255 randomly selected US adults (age 18 or older), 1787 of them use the Internet regularly. Of the Internet users, 1054 use a social networking site. Find and interpret a 95% confidence interval for each of the following proportions:

(a) Proportion of US adults who use the Internet regularly.

(b) Proportion of US adult Internet users who use a social networking site.

(c) Proportion of all US adults who use a social networking site. Use the confidence interval to estimate whether it is plausible that 50% of all US adults in 2011 use a social networking site.