Question

A convenience sample differs from a voluntary sample in that

a convenience sample is structured based on accessibility to the researcher, and a voluntary sample is based on participant interest.
convenience samples survey each participant once, and voluntary samples survey each participant numerous times.
convenience sampling is a method of random sampling, and a voluntary sample is not.
convenience sampling is not a probability-based method, and voluntary sampling is.

Answer 1

The best answer to the incomplete statement above would be the first choice. A convenience sample differs from a voluntary sample because a convenience sample is based on how accessible or easily obtained participants are to the researcher, while a voluntary sample is based on the participants' interest of participating. 

Answer 2

Answer: A convenience sample is structured based on accessibility to the researcher, and a voluntary sample is based on participant interest.

Explanation:

For the conventional sample the researcher chooses a sample that is readily available in some non-random way. Thus, it is structured based on accessibility to the researcher.

But for the voluntary sample the researcher puts out a request for participants of a population to join the sample, and participants decide whether or not to be in the sample. Thus, it is based on participant interest.