______ a teacher, his main duty is to help the students become better learners.
—Were you at Mary’s party last night?—No, I ____________ my sister. She met with difficult problems.
My grandparents____ in that city since 2008.
一Oh,there’s someone knocking at the door. 一 must be that naughty boy.
We can’t do it that way --- but whether it will work is ______ matter.
--- ______will the invitations be sent to our guests? --- In three days.