Given a sentence, fill out the missing word with a 'no' or a number (between zero and ten). You should write the numbers with english alphabet, like: four instead of 4.

[EX Q]: Norplant implants are ____ matchstick size rods that are inserted into the upper arm.
[EX A]: six

[EX Q]: Pyrimidines contain ____ ring and purines contain two rings.
[EX A]: one

[EX Q]: Hydra has ____ cell lineages, which are all self-renewing and maintained by stem cells.
[EX A]:
three