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

[Q]: Pelycosaurs are a paraphyletic group of _ primitive families of synapsids.
[A]: six


[Q]: Lightning can travel _ miles or more horizontally from the storm, then strike the ground.
[A]: six


[Q]: Female bats suckle their young with milk and weaning usually occurs at the age of _ to six weeks.
[A]:
four