During the first half of the twentieth century, the average American household was ______ by the introduction of a group of machines that profoundly altered the daily lives of housewives.

A．the dust-jackets of some books are very attractive
B．you start reading one of the books
C．it is raining outside
D．you have to make sure you don’t buy a dull book as a present

A．had a lawful lover
B．was an illegal writer
C．used to be a lawyer
D．was a competent doctor