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

[EX Q]: Diarrhea is an illness that kills _ and one-half million children per year.
[EX A]: three

[EX Q]: Retinoic acid regulates oral epithelial differentiation by _ mechanisms.
[EX A]: two

[EX Q]: Babies usually start sleeping through the night sometime between eight weeks and _ months of age.
[EX A]:
six