Laws that require vehicles to have catalytic converters or that restrict or prohibit leaf burning are:

A) Pigouvian taxes.
B) internalization of externalities.
C) transaction costs.
D) environmental standards.

Laws that require vehicles to have catalytic converters or that restrict or prohibit leaf burning are examples of environmental standards. These standards are put in place to minimize negative externalities, such as air pollution, and promote public health and safety. They differ from Pigouvian taxes in that they do not involve a monetary penalty for negative externalities, and from internalization of externalities in that they are not market-based solutions.