who疑問代詞,既可指單數,又可指複數,應根據不同的語境來判斷。如:-Who is the little girl
-He is my little sister Mary. 這裏的“who”指的是“the little girl”,所以是單數。又如:-Who are they?-They are my parents. 這裏的“who”指的是they,所以是複數。所以who的單複數是由指代的人或物而定的。
who的複數形式還是who,不過be動詞要變。
比如 Who is he/she? 變為複數: Who are they?