Final answer:
Word-of-mouth referrals would have the lowest cost to the broker compared to other promotions like television advertisements, social media marketing, and local newspaper ads. So, the correct answer is option a.
Step-by-step explanation:
The promotion with the lowest cost to the broker would be word-of-mouth referrals. This is because word-of-mouth referrals rely on individuals spreading the message about a product or service through personal recommendations, without any direct cost to the broker. Other promotions like television advertisements, social media marketing, and local newspaper ads usually involve financial expenses for the broker.
So, the correct answer is option a.