Du solltest die Sätze in ein Array packen.
Die 5 Elemente sollten die selbe Klasse haben.
Ich gehe jetzt mal davon aus, dass die Elemente
window.addEventListener("load", function() {
var sentences = [
["Sentence-1 for 1st Element", "Sentence-2 for 1st Element", "Sentence-3 for 1st Element"],
["Sentence-1 for 2nd Element", "Sentence-2 for 2nd Element", "Sentence-3 for 2nd Element"],
["Sentence-1 for 3rd Element", "Sentence-2 for 3rd Element", "Sentence-3 for 3rd Element"],
["Sentence-1 for 4th Element", "Sentence-2 for 4th Element", "Sentence-3 for 4th Element"],
["Sentence-1 for 5th Element", "Sentence-2 for 5th Element", "Sentence-3 for 5th Element"]
];
var elements = document.getElementsByClassName("yourClass");
for (var i = 0; i < elements.length; i++) {
elements[i].removeChild(elements[i].childNodes[0]);
var randomNumber = parseInt(Math.random() * 3);
var randomText = sentences[i][randomNumber];
var randomTextChild = document.createTextNode(randomText);
elements[i].appendChild(randomTextChild);
}
}, false);
"yourClass" musst du halt ersetzten.