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

[EX Q]: Females inherit _ X chromosomes, one from each parent.
[EX A]: two

[EX Q]: Most women have _ problems getting pregnant with a retroverted uterus.
[EX A]: no

[EX Q]: Some vaccines take up to _ weeks to become effective.
[EX A]:
four