-Has Tommy finished his homework yet?-I have no idea; he ____ it this morning.
--- How did your students express their thanks to you on Teachers’ Day? --- A gift, together with many flowers ______ sent to me by my students.
--- Why do you look sad? ---There are so many problems ______.
--- What has happened here? --- There was ______ accident here about an hour ago. ______ car hit a tree and ______ driver was killed.
We can’t get the machine to run. There must be ______ with it.
Only ______according to the directions can the medicine be quite effective.