JS Quiz: Medium: Object key coercion collision

[Yoshiii]

What does this print?

const a = {};
const b = {};
const obj = {};
obj[a] = 'first';
obj[b] = 'second';
console.log(Object.keys(obj).length, obj[a]);

• 2 first
• 2 second
• 1 first
• 1 second