Here is the answer to the given question above. Based on the given sample sentences, the best way to combine the sentences using a semicolon would be this: <span>The world’s nations must cooperate; one nation cannot solve the world’s problems by itself. The correct answer would be the second option. Hope this helps.</span>
Present perfect tense. Have washed is the verb, Have or Has is used to show an action that has taken place in the present, not quite long or is still taking place
