Change element display by class name

    function showStuff(id) {
        document.getElementById(id).style.display = 'block';
    }
    function hideStuff(id) {
        document.getElementById(id).style.display = 'none';
    }

    function showStuff(id) {
        // you could do this with a for or while loop, as well... that would be less repetition and reduce memory usage
        new hideStuff('question1');
        new hideStuff('question2');
        new hideStuff('question3');
        document.getElementById(id).style.display = 'block';
    }
    function hideStuff(id) {
        // or... use document.getElementById(id).className; that's what your really asking in your question, but you will need to add your css classes for this to work
        document.getElementById(id).style.display = 'none';
      }
    }