Since it's a multiple choice question, one assumes there is a correct answer, and presumably that is A, because there is a clear argument for it (you wish to sample from the population distribution, which can be viewed as a mixture of an initial-respondents distribution and an initial-non-respondents distribution and so you cannot claim to have sampled from the mixture until you've sampled from both mixture components, since they are probably statistically distinct).

Tangentially though, a big question here is how wise it is for the US education system to be based so heavily on multiple choice questions. There are other countries with decent education systems that do not do this.