In circumstances involving millions of emitters of small amounts of pollution who have no strong interest in trading, will typically offer a better choice for achieving desired reductions of environmental pollution levels.

Pollution charges

Explanation:

In circumstances involving millions of pollution emitters of small amounts, it is much easier and simpler to implement policies involving pollution charges. This allows the society to reflect on the economic cost of pollution along with the environmental consideration. In a way, pollution charges affect the economic behavior of the polluters and by doing this, it is likely to achieve the desired reductions of environmental pollution levels. Pollution charges have now become a common economic tool across the world for environmental pollution reduction.

the answer is b: a lockout