Which of the Following Is an Example of the Measures

Which of the following is an example of the measures that European governments undertook in the late twentieth century to address environmental problems?

A) They began developing corn-based ethanol as an alternative fuel source.
B) They stopped using nuclear power in order to prevent toxic nuclear waste from entering the environment.
C) They encouraged more people to start using airplanes as transport in order to avoid automobile emissions.
D) They developed car-free zones in urban centers and added bicycle lanes and pedestrian spaces.