1. who? mübtəda və tamamlıq sualıdır. fərqi ondadır ki,tamamlıqda who?+sözönü = sözönü+whom? olur.
sözönləri (by,for,from,at,about,with,to) ayrılıb sona gedəndə who şəklini alır: who ... by? (= by whom .....?
who were the doctors assisted by during the operation? = by whom were the doctors assisted during the operation?
who did the policeman explain the rule to ? = to whom did the policeman explain the rule?

belə cümlələrdəki tipik səhvlərə sonuncu cümlə üzrə baxaq:
whom to did the policeman explain the rule? (to whom olmalı idi, whom did the policeman explain the rule? (to ilə olmalı idi);
whom did the policeman explain the rule to? (to sonda who ilə olardı); who did the policeman explained the rule to? (explained did ilə olmaz); who the policeman did explained the rule to? (sıra səhvdir-did the policeman olmalıdır)