When _____ the abacus _____ — In the sixth century by the Chinese people.

The great success of this program has been _____ due to the support given by the local businessmen [ ]

Her life ________ a lot during the lastthree years.

rd to ________ the green beans from the red ones, because there are too many of them.

John is ______ honest boy. He has ______ useful book.