JavaScript Riddle

HTML

<script src="http://google-code-prettify.googlecode.com/svn/trunk/src/prettify.js"></script>
<script src="https://raw.github.com/LeaVerou/prefixfree/master/prefixfree.min.js"></script>

			<form id="respostas" method="POST">
     			<h5 class="texto_pergunta">
     				1) Quais dessas empresas não são bandeiras?

     				<p class="conceito" resposta="resposta0" hidden></p>	
     			</h5>
     			
				<div class="respostas">
					<div class="custom-control custom-radio">
						<input type="radio" id="0_a" name="resposta0" class="custom-control-input" value="a">
						<label class="custom-control-label" for="0_a">
							Elo
						</label>
					</div>
					<div class="custom-control custom-radio">
						<input type="radio" id="0_b" name="resposta0" class="custom-control-input" value="b">
						<label class="custom-control-label" for="0_b">
							Banrisul
						</label>
					</div>
					<div class="custom-control custom-radio">
						<input type="radio" id="0_c" name="resposta0" class="custom-control-input" value="c">
						<label class="custom-control-label" for="0_c">
							Visa
						</label>
					</div>
					<div class="custom-control custom-radio">
						<input type="radio" id="0_d" name="resposta0" class="custom-control-input" value="d">
						<label class="custom-control-label" for="0_d">
							Hiper
						</label>
					</div>
				</div>

				<center>
					<button type="submit" class="btn btn-primary botao_enviar">
						Enviar
					</button>
				</center>
			</form>
		</div>
	</div>
</div>

JavaScript

var x = document.getElementsByTagName("input");
var i;
for (i = 0; i < x.length; i++) {
    x[i].disabled = true;
}