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

[EX Q]: Stroke is our nation's number _ killer, and a leading cause of disability for older adults.
[EX A]: three

[EX Q]: Autism is _ to four times more likely to affect boys than girls.
[EX A]: three

[EX Q]: Some babies start sleeping through the night on their own around three or _ months.
[EX A]:
four