Okay, I'm replying without reading the other replies, so I apologize if this is redundant...
My answer choice is B, scroll down for why.
Most radicals who argue for violent revolution and complete overthrow of our existing society have no clear idea what will emerge from the destruction. They just assert that things are so bad now that any change would have to be a change for the better. But surely this is mistaken, for things might actually turn out to be worse.
...what's wrong with this argument? ... it provides no support for the conclusion... so look for an answer choice that says "hey you didn't give even one premise that supports your conclusion that 'things might turn out to be worse'"
The most effective point that can be raised against this argument is that the author says nothing about,
(B) the specific results of the revolution that would be changes for the worse.
"Really, they might turn out to be worse? How? Give me a specific result of the revolution that would be a change for the worse"
Actually this one was pretty easy, because once you've identified the conclusion, it's pretty easy to eliminate all the other answer choices..