I hope this answer is what you are looking for:
You can make an array with your answers, and then check to see if the given answer is inside the array.
const array = ['test', 'test2', 'test3'];
if (array.includes(an.value.toLowerCase() ) )
...
Something else, you are missing a semicolon in your else { … }.
bt.innerText = "Wrong!";
solved How I can Create many answer [closed]