7135/2 Economics Jun 2016 Quiz | AQA AS Level MCQ

In the following diagram D$_1$ shows the market demand for smoke alarms when consumers have imperfect information about the benefits of installing a smoke alarm. If consumers had full information, thearket demand for smoke alarms would be D$_2$.
Which one of the following policies is most likely to ensure that consumption and production of smoke alarms are at the social optimum level?