If we're going to bother to ask (b) at all, it's probably best to frame it in a way that doesn't make "some but not all of them" the obvious answer.

For example, perhaps you could identify some groups you consider definitive of Feminism and Social Justice, and we could ask "How often do you agree with $group?" (IIRC, on their own blog Yvain often uses something called jezebel as a metric for what feminists believe.)