Politicians can gauge public opinion by looking at?

The most definitive answer is by taking public opinion polls.

Explanation: There are many ways to gauge public opinion. In Russia, public opinion was measured by the Secret Police who basically told people what they thought. In the United States, a variety of methods are used.All politicians today use polling, interviewing potential voters as to their popularity and the popularity of their programs. Elections are a way to gauge public opinion. Donald Trump successfully won for President in 2016 because voters liked his programs. In 2018, a number of Governors, Senators, and Congressmen who were Trump supporters lost their election as voter views changed. Lobbyists and interest groups gauge public opinion, but then try to sway it to their beliefs.  

your answer would be a) no nation can be economically self-sufficient.

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