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

Ex Input:
Blood is made up of _ parts.

Ex Output:
four


Ex Input:
Animals develop either two or _ embryonic germs layers .

Ex Output:
three


Ex Input:
Hamstrings are a group of _ muscles at the back of the thigh that attach to the hip and the knee.

Ex Output:

four