Which of the Following Is a Disadvantage of Conducting a Public

Which of the following is a disadvantage of conducting a public opinion survey over the phone?

A) Unlisted numbers cannot be reached by telephone polls.
B) Federal law prohibits the use of automated random-digit-dialing programs to unlisted numbers.
C) People are substantially less willing to participate in polls over the telephone than in person.
D) Independents are less willing to participate in polls over the telephone than are partisans.