Which of the Following Provides an Example of Command-And-Control Regulation

Which of the following provides an example of command-and-control regulation?

A) ​Taxing producers based on the external costs created by their pollution, thus internalizing external costs.
B) ​ Requiring firms to reduce their pollution by 50 percent, thus allowing them to emit 50 percent of their historical emissions, and allowing them to freely buy and sell allowances.
C) ​Requiring firms to use a particular type of pollution-control technology, such as smokestack scrubbers or catalytic converters.
D) ​Subsidizing firms that exceed their pollution-control targets.​