You can’t imagine what great trouble they have _____ the problem _____.
_____his father had come, his face lit up.
______, they would certainly come and help us.
-How long ______ each other before they ______ married? --For about a year.
Smith ______ a book about China last year, but I don't know whether he has finished it.
I paid him $ 50 for the painting , but its true ___ must be least $500.