Consider the short term rental market between homeowners and renters. There are many different kinds of externalities in this market. From the article, "[h]otel, hostel and bed and breakfast operators say private home letters have an unfair advantage bypassing costs and fire regulations, and pose potential risks for safety of guests and owners." What kind of externality is it about? (Please explain clearly! Thanks)

(a) Positive externality in production.

(b) Negative externality in production.

(c) Positive externality in consumption.

(d) Negative externality in consumption.