I keep getting a score of '0'. how do I fix my scoring section/what did I not do to my code?

/* QUIZ
Experimenting with if/else statements in a quiz format with a score */

//questions 1-5 prompt with an alert and score
var question1 = prompt("What color is the sky?");
  question1 = question1.toUpperCase();

if (question1 === 'BLUE') {
  alert("WOOT!");
  score += 10;
} else {
   alert('nope, it is blue.');     
   }

var question2 = prompt("How many legs does a horse have?");
question2 = question2.toUpperCase();

if (question2 === '4') {
    alert("WOOT!");
    score += 10;
} else {
  alert('nada, there are 4 legs.');
}

var question3 = prompt("What is a 'two-legged' ?");
question3 = question3.toUpperCase();

  if (question3 === 'HUMAN') {
    alert("WOOT!");
    score += 10;
  } else {
    alert("negative, it is a human.");
  }

var question4 = prompt("Name the best food at McDonald's.");
question4 = question4.toUpperCase();

if (question4 === 'FRENCH FRIES') {
  alert("WOOT!");
  score += 10;
} else {
  alert("nil, the correct answer is french fries.");        
}

var question5 = prompt("Can you ride a giraffe?");
question5 = question5.toUpperCase();

if (question5 === "YES") {
  alert("WOOT!");
  score += 10;
} else {
  alert("haha, yes you can!");
}

//score keeping
var score = 0;
  if (score === 50) {
    alert("Your score is " + score);
    alert("PERFECT SCORE");
  } else if (score <= 40) {
    alert("Your score is " + score);
    alert("GOOD");
  } else if (score <= 30) {
    alert("Your score is " + score);
    alert("OK");
  } else if (score <= 20) {
    alert("Your score is " + score);
    alert("NOT GREAT");
  } else {
    alert("Your score is " + score);
    alert("YOU'RE KILLIN ME SMALLS!");
  }