Let's guess what's the correct preposition (on, at, in). Create as bookmarket with it :)

preposition_game.js

function printSolution(element) {
    let answer = element.getAttribute("data-answer");
    let selectedOptions = Array.from(element.selectedOptions).map(e => e.text);
    if (selectedOptions.includes(answer)) {
        element.style.border = "2px solid green";
    } else {
        element.style.border = "2px solid red";
    }
}
let prepositions = ["", "on", "at", "in"];
let prepOptions = prepositions.map(p => `<option>${p}</option>`);
let prepSelect = `<select data-answer="$1" onchange="printSolution(this)" style="border: 2px solid black">${prepOptions}</select>`;

let paragraphs = document.getElementsByTagName("p");

for (let p of paragraphs) {
    p.innerHTML = p.innerHTML
                   .replace(/\b(on|in|at)\b/g, prepSelect);
}