In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.

Q: Infinity divided by _ is infinity.

A: two
****
Q: Plasma levels fall by about a half within three to _ hours.

A: four
****
Q: Plazas have _ accumulations of rubbish but are covered with even layers of mud bricks and plaster.

A:
no
****