Ok, PT #06 - Oct 1992
The flaw is as someone has said that the argument takes for granted that what the security guards says is a fact. This could be true, but it doesn't have to be. The question doesn't ask anything about the burglary itself, you're just supposed to find an argument with a similar flaw. That means, you have to find a flaw where some person or entity makes a claim and that the conclusion assumes that claim to be factual without further proof.
Alternative b) to this question is the correct answer, because the argument assumes that the store's competitors are correct, without any further evidence supporting that.