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

[Q]: Human sperm comes in _ varieties, mixed.
[A]: three


[Q]: Plazas have _ accumulations of rubbish but are covered with even layers of mud bricks and plaster.
[A]: no


[Q]: Dietary supplements are particularly important for older people for _ reasons.
[A]:
three