Explanation:

- Restrictive trade barriers: These are obstacles that limit free trade, such as tariffs and quotas. They typically restrict market forces rather than promote them.

- The right to withhold labour: This refers to labor actions like strikes. While it influences the labor market, it is not a market force itself.

- Open competition: This is a core market force. It drives innovation, efficiency, and consumer choice by allowing businesses to compete freely.

- None of the above: This would apply if none of the options described market forces, which isn’t the case here.