This could be true. The stimulus tells us that some people think there are a few rotten politicians. This implies some people do not think there are a few rotten politicians. Members of this latter group may think all politicians are rotten.

This could be true. All we know is that effective politicians are not scrupulously honest—we don’t know anything about the character of ineffective politicians.

This could be true. We don’t know anything about how people do or don’t define a politician’s job.

This could be true. We only know that all effective politicians are deceitful. We don’t know anything about ineffective politicians and whether or not they’re deceitful.

This must be false. The stimulus says that if you’re scrupulously honest you cannot be an effective politician. It is therefore impossible for there to be politicians who are both scrupulously honest and effective.