documentclass[addpoints]{exam}
printanswers

begin{document}

begin{questions}
question Which of these guys invented time?
    begin{choices}
        choice Stephen Hawking
        choice Albert Einstein
        choice Isaac Newton
        correctchoice This makes no sense
    end{choices}

    question
    What is the way to write down the function for cubic power?
    begin{choices}
        choice  $f(x) = x$
        choice  $f(x) = x^2$
        correctchoice  $f(x) = x^3$
        choice  $f(x) = x^4$
    end{choices}
end{questions}

end{document}