The correct answer is: "promoting industrial growth".
Laissez-faire supporters believed that the most efficient economic outcomes were reached by the free interactions of economic agents (households, firms and public sector entitities) in the markets, and that external goverment interventionism distorted such outcomes, that maximized the welfare of all the market participants.
Therefore, protecting farmers, expanding union membership and preventing foreign competition cannot be measures supported by advocates of laissez-faire policies because they describe forms of interventionism.