Final answer:
In 2017, China had the most restrictive Internet censorship policies, which blocked citizens from using various international social media platforms and censored topics considered harmful by the state.
Step-by-step explanation:
In 2017, the country with the most restrictive Internet censorship policies, effectively blocking its citizens from conducting Internet searches and from using social media platforms, was China. China's stringent control over the Internet, known as the Great Firewall of China, blocks access to various sites to suppress what the government considers "harmful information." This includes topics like dissent against government politics, discussions on China's relationship with territories such as Hong Kong and Tibet, and criticism of government actions. Despite these restrictions, the nation's Internet users rely on local media companies, and the government maintains a presence on social media to disseminate its messages.