উত্তর সিলেক্ট করলে সঠিক ও ভুল দেখাবে।
ব্যাখ্যা ও সঠিক সমাধান
উত্তর:
By whom has the work been done?
In passive voice, by should be placed before noun. Here whom is a passive form of Who and by is added with that. So we have BY WHOM. Then the remaining is as usual that you already know (the conversions)