可以. 先说who, 主语从句：Who killed the man is still a mystery(谜团). 这是一个主语从句. 同位语从句：The question who will take his place is still not clear.（who作主语）,是主语的同位语. 再说how, 主语从句：How he killed the man is still a mystery(谜团). 这是一个主语从句. 同位语从句：The question how he killed the man is still not clear.（who作主语）,是主语的同位语.
