As a citizen, you have certain responsibilities such as obeying the law. Which is NOT a law enforced by the government?

A. The sale of cigarettes to minors is prohibited.
B. Children are required to receive formal schooling for a certain period of time.
C. Drivers must obtain a license before operating a motor vehicle.
D. All citizens are required to vote in presidential elections.

To find out which option is NOT a law enforced by the government, we need to understand the laws mentioned in each option.

A. The sale of cigarettes to minors is prohibited.
This is a law enforced by the government. Selling cigarettes to minors is illegal in most jurisdictions.

B. Children are required to receive formal schooling for a certain period of time.
This is also a law enforced by the government. In many countries, there are compulsory education laws that require children to attend school for a certain period of time.

C. Drivers must obtain a license before operating a motor vehicle.
This is another law enforced by the government. Before driving a motor vehicle, individuals are required to obtain a valid driver's license.

D. All citizens are required to vote in presidential elections.
This is NOT a law enforced by the government in most democracies. While voting is encouraged and seen as an important civic duty, it is not mandatory for all citizens to vote in presidential elections in most countries.

Therefore, the answer is D. All citizens are required to vote in presidential elections.