The argument is discussing how Grenier is perceived as insincere by voters and concludes that she will likely lose the election.
Answer choice A states that voters will likely not vote for a politician they deem to be insincere. This would follow perfectly in combination with the other premise towards the conclusion.
If they think she is insincere and they tend not to vote for who they think is insincere, then she will most likely lose the election.
Answer choice B says that voters are unlikely to be aware of a change in a politician's stance. But clearly based on the argument, the voters did notice her change in stance because they think she is being insincere.
Let me know if this helped, and please ask if you have any other questions.