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]: Couples spend ____ billion dollars a year on infertility treatments.
[EX A]: two

[EX Q]: Prions are protein molecules which have ____ metastable states.
[EX A]: two

[EX Q]: Fibreoptic systems have an effective life ____ times that of copper.
[EX A]:
three