DENVER — One of three suburban Denver girls who authorities say tried to
join Islamic State militants in Syria was confused about what her role would
be if she had actually made it there, the girl's father said Tuesday.
请问此处的who authorities，我感到疑惑的是
(1) authoritity 不是只有名词解吗? 如果用法是who authorities 不就怪怪的?
(2) 此处who authorities 是做如何解呢?
以上，谢谢指点