The accurate statement about nation-states is:
In the modern world, most countries are nation-states.
To elaborate, while not all countries are nation-states (as some may encompass multiple nations or ethnic groups), many countries today are considered nation-states, where the political boundaries align closely with the cultural or ethnic identity of a particular nation. The other statements are inaccurate; for example, the first nation-states emerged earlier, particularly in the early modern period, not the twentieth century, and a country does not need to have two official languages to be considered a nation-state.