Okay, so what is the purpose of making an experiment single blind or double blind? When we make an experiment blinded in some way, the participant and/or the researcher does not know what condition the participant is in, and basically that reduces the odds of them behaving in a biased way. Remember, if our experimenter behaves in a biased way, that's called an experimenter effect, and if our participant is behaving in a biased way, that could be the result of demand characteristics, basically them guessing what condition they're in and what the independent variable and dependent variable are, and then acting in a way that they think the experimenter is going to want them to act. If they don't know what condition they're in, the odds of that are greatly reduced. And so, based on that, our answer here is going to be b.
By making an experiment either single blind or double blind, it can reduce potential bias from the participants and/or researchers, which could influence the results, and we don't want that happening. So, our answer here is b.