A venomous snake designated the emblem of the rebellion by the insurge

I don't think the issue is important -- the GMAT will never test you on the correct usage of the word "designate" -- but I don't think the OA here is right. It's certainly possible to sometimes use "designate" without "as", but in the particular meaning this sentence intends, I think the "as" is required. There's some chance I'm wrong about that, though, and the question isn't important enough that I'll be inclined to look into it further. I'm not sure what purpose this question was meant to serve, but there's nothing at all wrong with answer D here, so if B is correct (something I'm not sure of) the question would have two right answers. There's no way to guess what verb tense this sentence means to use.