Me asap pls : )
a researcher places a radio advertisement offering $32 in exchange for participation in a short study. the researcher accepts the first nine people who respond
to the advertisement. which of the following statements is true about the sample?

a. it is a valid sample because the first nine people were selected to participate.
b. it is not a valid sample because it is not a random sample of the population
c. it is a valid sample because money was offered to participants
d. it is not a valid sample because it is only a short study