The past progressive is most useful when?
a. when an action happened in the past
b. when an action was uninterrupted in the past
c. when an uninterrupted action happens
d. when an action gets increasingly common
i have read that past progressive are interrupted actions so that only leaves a anddoes anyone know the correct answer

The greatest gift the sumerians gave the world was the invention of writing. the sumerians were wealthy people. they needed some way to keep track of what they owned. they began drawing pictures. they used a reed as a pen. they drew on soft pieces of clay. the soft clay was then dried in the sun. the tablet became a permanent record. later, the sumerian drawings changed into wedge-shaped symbols. this kind of writing is called cuneiform. by putting symbols together, the sumerians could write entire sentences.