When I click the submit button, nothing happens.

function random_number(num) {  // New function called random_choice that takes one parameter, num (or a number)
    // Get a random number between 0 and a passed-in number
    var num = num || 4  // If no number passed in, default to 4
    return Math.floor(Math.random() * num); // Round the answer down (floor) of a random number between 0 and 1 and multiply it by a number. Then return a value and exit the function.
}

function mash_choice() {  // New function called mash_choice that doesn't take any parameters 
    // Since MASH is a special case, give it its own list
    var mash = ['cardboardbox', 'tent', 'apartment', 'house'];  // The array of choices to pick from 
    var randomNum = random_number(4);  // Use the above function to get a number between 0 and 4
    return mash[randomNum];  // Return the list item the random number function just picked and exit the function 
}

function get_answer(category) { 
    // Get a random answer from the available answers in a given category
    var choices = [];  // A blank array to hold the user provided answer  
    var selector = 'input[name="' + category + '[]"]';  // Build a CSS selector for the blanks in our passed in category 
    var inputs = document.querySelectorAll(selector);  // Get all of the inputs that match our selector 
    var answer;  

    for (var i = 0; i < inputs.length; i++) {  // Begin a for loop that will run through the code. i++ = add one to the counter which is "i"
        answer = inputs[i].value;  // Get the input with the index value of the counter and get the value ie. if they typed in dog, you get back "dog" 
        if (answer !== '') {  // If answer doesn't equal a blank... !== means doesn't equal 
            choices.push(answer); //...add it to the end of the list 
        }
    }
    return choices[random_number(choices.length)];   // Pick and return a random choice choice.length = number of answers the user provided in that category 
}

function fill_in_answers(answers) {
    // Find the spans that need filled
    var mash = document.querySelector('#mash');  // This says make a new variable and find the HTML tag that has the ID of "home" 
    var job = document.querySelector('#job');
    var cats = document.querySelector('#cats');
    var animals = document.querySelector('#animals');
    var single = documentnet.querySelector('#single');

    // Fill them with the provided answers
    mash.innerText = answers['mash'];
    job.innerText = answers['job'];
    cats.innerText = answers['cats'];
    animals.innerText = answers['animals'];
    single.innerText = answers['single'];
    mash.innerHTML = answers.mash;  // Change the content of the element in the HTML doc with the id "home" to the "mash" value in answers 
    job.innerHTML = answers.job;  // Change the content of the element in the HTML doc with the id "career" to the "career" value in answer
    cats.innerHTML = answers.cats;
    animals.innerHTML = answers.animals;
    single.innerHTML = answers.single;
}

function handle_submission(evt) {
    evt.preventDefault();  // Stop the form from reloading the page 
    evt.stopPropagation();  // Stop the form from reloading the page

    // Build up our answers object
    var answers_object = {
        'mash': mash_choice(),
        'job': get_answer('job'),
        'cats': get_answer('cats'),
        'animals': get_answer('animals')
        'single': get_answer('single')
    }
    // Fill in the answers
    fill_in_answers(answers_object);

    var answer_div = document.querySelector('#answers');
    answer_div.classList.add('show');
}

// Find the form on the page and attach a handler for when it's submitted
var form = document.querySelector('#mash');  
form.addEventListener('submit', handle_submission);  // Anytime the form is submitted, we want to call the function handle_submission