is on duty today

is on duty today what is on duty today? who is on duty today Who is on duty today?为什么用on duty Who is on duty today ?是什么意思 谢谢 whose turn is it ( ) on duty today who is on duty today怎么回答 l think lily is on duty today.对 lily is on duty today提问 Nobody is ( )duty today. who is ( ) duty today? whose turn is it-------（be） on duty today ____is on duty today?Li Lei is.怎么填?